Koh Samui
Koh Samui is Thailand's second most popular vacation island after Phuket, and it's nearly as developed, too. Unlike the other islands in the Koh Samui Archipelago, it has an airport.
Koh Samui is a large island (the second largest in Thailand) and is home to a wide variety of places to stay across all budgets. It's also home to lots of bars and restaurants, including some upscale eateries operated by famous chefs. Compared to neighboring islands, Samui stays busy with a crowd of higher budget travelers, honeymooners, and families on vacation. The nightlife in Chaweng gets rowdy; thankfully, Koh Samui is large enough for escaping to tranquility, too.
Though the beaches are not quite as beautiful as those on islands along the Andaman Coast (Phuket, Koh Lanta, and Koh Phi Phi), they offer visitors warm water, soft sand, and lots of palm trees. The interior of Koh Samui remains mostly mountainous and undeveloped jungle.
Ko Pha Ngan
This notorious party island isn't just about getting wasted on Haad Rin Beach and dancing till dawn in the sand during Full Moon Parties. Koh Pha Ngan is a big island with plenty of other beaches and idyllic bays on offer. Regardless, Koh Pha Ngan tends to draw a younger, backpacking crowd along with long-term travelers and digital nomads in search of holistic communities and cheap living. The Sanctuary is a boat-accessible health retreat tucked in a bay just around the corner from the party peninsula of Haad Rin.
The southern part of Koh Pha Ngan is known for its parties where body paint and electronic music get showcased. But the island also has some beautiful, quiet beaches with seaside bungalows and high-end boutique resorts. The northern side of the island has some bays that cater to a more relaxed crowd. When no party is in progress, the beach at Haad Rin is excellent. Travelers tend to head over to little Koh Tao to play between Full Moon Party weeks.
Koh Tao
Although it was once reserved for divers and backpackers, Koh Tao is becoming more and more popular with vacationers. Koh Tao is the most popular place in the world to become scuba certified, and doing so is surprisingly inexpensive; dive shops crowd for space among bars and restaurants.
Koh Tao may have been "sleepy" back when when the divers who came to the island had morning classes and early dives to make. Now, a nightly pub crawl and plenty of pubs attract travelers from Koh Pha Ngan after the Full Moon Party week finishes. The island can get rambunctious with bucket drinks, fireshows, and numerous pubs on streets away from the beach.
Koh Tao is located north of Koh Pha Ngan and is smaller and lesser developed than either of its neighbors in the Koh Samui archipelago. That doesn't mean you'll have to rough it; there are enough resorts and restaurants to keep you occupied and entertained.
Ang Thong National Marine Park
The three islands of the Koh Samui Archipelago are also part of Ang Thong Marine National Park, one of Thailand's protected nature areas. There are actually 42 separate islands spread over 49 square miles that make up the marine park. Most are very small and can only be visited on day trips. Snorkeling is excellent over the shallow reefs in the park. Paddling around the islands by kayak may yield your own private beach hidden just out of sight.
Koh Wua Talap is home to the marine park headquarters and tourist center. If you're willing to go without electricity after 11 p.m., you can actually reserve one of the few bungalows on the island for beautiful views all to yourself in the morning. Camping is also available, and no, there isn't any Wi-Fi!
The best way to see Ang Thong Marine National Park is to arrange a day trip from one of the islands. Koh Samui is the usual base, although boats can be hired from Koh Pha Nagan and Koh Tao as well. Most travel agents and hotel concierges will gladly sell you a ticket.