Understand
The word khao san itself means milled rice and is an attribution to the historical role of this street in the rice trade. The first business to open on Khao San Road was a small hotel aimed at serving civil servants from the provinces who came to Bangkok on business. The hotel was followed by Sor Thambhakdi, a shop selling monks' accessories. It was followed by four similar businesses, and Khao San became known as a "religious road".
Word soon spread about the easy lifestyle and friendliness of the locals. Friends told friends, and before long, the owner of the house started to charge 20 baht for food and lodging. The first commercial guesthouse, called Bonny, opened with six small bedrooms.
Today, there's a lot more than six small bedrooms on offer. In the span of just a couple of blocks, there are bars, food stalls, restaurants, convenience stores, pharmacies, Internet cafés, money changing booths, ATMs, shoe stores, massage parlors, tailors, travel agencies, laundry, boxing gyms, optometrists, endless warrens of suspiciously discounted designer clothes and, oh, rooms for the night.

Come in
Khao San Road is fairly easy to get to from anywhere in Bangkok. Taxis, buses, and river ferry are your main options. While the metro and the skytrain are convenient ways of getting to many places in Bangkok, there is unfortunately no train (yet) that will take you near Khao San Road (or anywhere else on Rattanakosin Island, for that matter)

See
There are a lot of famous historical sites to speak of, Khao San is on the Rattanakosin island. Around the street, there are a number of old buildings and temples, some of which have been transformed into restaurants and even tattoo parlours, although you will still find quiet family homes if you look deep enough. Aside from some interesting architecture, Banglampoo shows the mix of peoples and heritages that is the character of Bangkok. There are Muslims, Buddhists, Mons, and of course a great number of foreigners in this small area. All of this makes the area an interesting place for a glimpse of Thai life. Thais also appreciate the area for the many types of traditional kanom or Thai snacks and desserts available and the cheap clothing available in the Banglampoo Market (see below).
At the bottom of Khao San is Wat Chana Songkram, which translates as "War Victory Temple". This area was formally given to the Mon peoples who helped the Thai fight off the Burmese centuries ago. The Mon set up a community here and built this temple as well. Many travelers use the temple grounds to connect between Khao San and Phra Athit Rd where the ferry pier is located. The temple is worth a visit, though, with nice murals, crisp sounding temple bells hanging from the eves, Bougainvillea vines and beautiful trees. There is no charge for admission and you are welcome to pay respect to the Buddha images or just find a little tranquility away from the throngs of backpackers on Khao San proper.
Famous sites within walking distance from Khao San Road include The Grand Palace (Wat Phra Kaew), Wat Pho, Sanam Luang Park, Chao Phraya river, Democracy Monument and The Golden Mount (Phu Khao Thong)

Enjoy

Sor. Vorapin Gym (13 Trok Kasap, Jakapong Rd., Panakorn, Bangkok 10200; tel. 662 282-3551) [1]. Offers morning (7:30am-9:30am) and afternoon (3:00-5:00pm) training in Muay Thai (Thai boxing) for 400 baht. Beginners and walk-ins are welcome. Shorts and gloves are provided. The English instruction may not be detailed, but key phrases like "punch", "kick", and "one-two" are in place. It's at the end of a dusty alley off Soi Rambuttri.
Suan Santichaiprakarn Park, just beyond Khao San Road, has a great view of the Chao Phraya river and the ultra-modern Rama VIII suspension bridge. In the evening, there are many activities going on in the park such as free aerobic exercise, the performing of Thai classical music, juggling, etc. The park has become a gathering place for new breakdancers to exchange their techniques. The park has one of the towers of the historical city wall of Rattanakosin. The canal on the otherside was part of the city moat. The park is on Pra Athit Rd, which has many old town houses that are now restaurants and cafés and near the river are a number of old smaller palaces now used by the likes of the FAO and Unicef.

Shopping Shopping Shopping!
The Banglamphu market is a good place to pick up cheap Thai knock-offs of everything from jeans to Italian sneakers, as well as a few posh Thai silk stores. (Not on Khao San but nearby, you can go to the bottom of Khao San, turn right and walk about 50 meters.) Food stalls also abound in this area. Khao San road is also home to many wholesale silver jewelry stores.
Aporia Books, 131 Tanao Road (road that runs at 'T' junction with Kao San Road - opposite end to the road with the stop for airport bus). Tel:+66-3-6292919. Has a good selection of both new and second-hand English titles, and offers a much more pleasant and organized environment for browsing than the other second-hand book shops on Khao San Road.


Eat

Khao San Road offers one of the most diverse food selections anywhere in Bangkok. Since the street sees such a varied nationality of travelers, several ethnic foods can be found here. Street carts that line Khao San Road sell decent phat thai (fried noodles), quail eggs, roti (like a pancake), falafel, hummus, various bugs and some sell just cocktails.
However, it's worth noting that much of it is specifically geared for backpackers — even the local phat thai, especially the 10 baht variety, economizes on the ingredients and uses soy instead of the traditional tamarind sauce. Those looking for truly good food would be advised to head elsewhere, such as to Sukhumvit.
As Khao San leaves its backpacker roots, standards (and prices) are rising. International outlets Burger King and Starbucks moved in during 2004.
Sunset Street. Located in the middle of the Khaosan Road, have few restaurants. Sunset Bar & Restaurant offer authentic Thai and International cuisine with live music performance on Thursday to Sunday. The most beautiful Starbuck Coffee also house in the Palace with more 100 year old history. Scoozi italian Pizza also provide home delivery to your comfort hotel room. Sabai Bar offers best Khaosan view while you are dining here.
Aquatini Riverside Restaurant, The Best riverside restaurant, is highly rated and great place to try many of thai food along with a great view of chao phra ya river. Jazz and Blue song is a concept of a restaurant, candle light, relaxation environment. it is the most romantic restaurant around Khaosan area.
Tom Yum Kung, The Best restaurant on khaosan road, is highly recommended and great place to try some tom yum gung (spicy shrimp soup).
Gulliver’s, on the west end of the road, is a decent sports bar with mid range pricing a good offering of Western food.
Silk Bar Pub & Restaurant, located in the middle of the khaosan road provide the BEST Khaosan view. Every day after 6pm, this place is packed with customers till very very late at night.
Sidewalk Café 1, a great outdoor people watching spot with a large menu.
May Kaidee's , on the road behind Aporia Books on Tanao Road (There are two 'T' junction roads at either end of Khao San Road; Tanao Road is the one at the other end to the road where the stop for the airport bus is located). This is one of the best vegetarian restaurants in the area and has been serving foreigners and hippie-types since 1988. May also runs a cooking class for 1200 baht/day; those interested need to give at least a day or so advance notice.
May Kaidee's 2, Samsen Road near Soi 1 [3]. An indoor air conditioned vegetarian restaurant with attached guesthouse - cheaper and cooler than May Kaidee's 1.
Number One. Located behind Aporia Books on Tanao Road. The restaurant offers a wide selection of vegetarian dishes.
Ethos International Vegetarian and Vegan Restaurant, on road behind Aporia Books on Tanao Road. [4]. A unique place with an attitude! No MSG, preservatives or artificial colours and flavours. Some organic dishes. Menu consists of Thai, Indian, Italian and Middle Eastern dishes. Excellent coffee and deserts. A comfortable place that attracts the spiritualist - yoga - conservation crowd. The restaurant also offers a public notice board for travelers use, Thai massage, Internet café and free Wi-Fi hotspot.
Popiang House. A "classic Khao San Road" Restaurant, which isn't really on Khao San Road, but on Soi Rambuttri, which is on the northern side of the Chana Songhkram Temple. You will find it by looking for the red plastic chairs and the yellow cheap tables. Its a great place to sip cheap beer too. Can be very busy in the night time. Good place to meet other backpackers. Offering a good selection of Thai food, and wonderful staff.
Wild Orchid is a good option that offers great green and red curries and delicious tom yum soups at low prices.
Oh My Cod!- An ultra clean & modern Brit owned British Café cum fish & chips shop situated in an oasis of peace off Soi Rambuttri, inside the bricked courtyard at the entrance to the Rambuttri Village Inn. Food is fresh and excellent (burgers, steak, fish, chips, eggs & more), prices low, plasma screen TVs at every table, staff friendly & helpful. The owner is knowledgeable and can direct you anywhere or obtain anything, special orders are accepted.
Prakorb's House, 52 Khao San Road (right side when walking from airport bus stop). Excellent food in this very friendly, family run hotel and restaurant - especially recommended are the vegetarian noodles.
Mr Yim's 2 Soi Chanasongkram. A small restaurant up a flight of stairs overlooking the wat. A wide selection of good quality food at good prices, including veggie options. The big baguettes are excellent value at 30B-70B ($1-$2 US).
147, 147 Tanao Road (next to the Burger King). Is an old standby serving excellent, cheap Thai dishes including vegetarian options.
Chabad Kosher Restaurant Ideal for Jewish travelers that keep kosher. The Chabad house is located on 96 Ram Buttri Street. There is a large meat menu with the opportunity to taste some great Kosher Thai cuisine (not the squashed fried squid on every street corner) or get a little schnitzel and hummous. The Chabad house also has a small store where you can purchase packet soups, matza, and other kosher items.

Drink
Khao San Road has some of the cheapest bars in town, and these days even some Thais head down to knock back a few. A can of Beer Chang is 25 baht at 7-11. Worth a look are a few street side VW vans converted to mobile bars, serving cocktails made from cheap liquor.
Bangkok Bar. Well liked pub round the corner from Khao San Road on Soi Rambuttri. Is attached to the "Sawasdee House" guest house.
Gullivers - A sports pub with billiards. Gradually turns into a rather wild dance party as the night wears on.
Lava, in the middle of Khao San. Go down the steps to one of the more modern and Western owned bars on the Road. Sunday nights are good.
Silk Bar, [5]. - One of the must-stop dining places on Khao San, with a view of the action on the street. Usually packed around 7-12 midnight.
Susies Pub - The pub that started it all. Owners of the pub have branched out to owning Austin Pub, Tom Yung Gung, and The Club. Usually packed and playing top 40s tunes.
The Club - The Best Club on Khaosan road, With a huge neon sign, you can't miss it. Interesting open design.
Mulligans Irish Bar - Opened in 2009 located upstairs in the Buddy Plaza with the classic motobikes on display. Mulligans servers the only cold pints on the Khao San Road. Mulligans have drinks deals nightly, live music and suprisingly is open 24 hours a day. out 12 baht. References from Wikipedia