Ton Sai is a beach near Krabi in Thailand, offering a combination of inexpensive accommodation and great rock climbing routes that make it popular with both backpackers and climbers alike. Compared to neighbouring Rai Leh and Ao Nang it's relatively rough around on the edges; in particular, the beach is unsuitable for swimming and becomes quite rocky as the tide goes out.
There's no overland access to Ton Sai, so all visitors arrive by boat. Rai Leh is a two minute long-tail ride or a 10-15 minute walk away, while long-tails from Ao Nang to Rai Leh will also stop at Ton Sai on demand.
There are three ways to reach Rai Leh on foot:
1) At low tide it's possible to walk around the rocky outcrop which separates Ton Sai from Rai Leh (10 minutes).
2) At high tide, most opt for the steep path which climbs up and over the rocky outcrop, which is densely covered with foliage (10 minutes).
3) The least used option is a longer trail which starts on the northern, forested, edge of Ton Sai and meanders past bungalows, thick jungle, and eventually to the back of Rai Leh, near the Diamond Cave area (20 minutes).
None of these options are possible at night without a flashlight/torch, and the jungle paths can be slippery and treacherous after the rain. At any time all three routes can be awkward and tricky for all but the fit and able-bodied so don't feel bad about taking the easy, scenic, and relaxing long-tail to get across.
The only way to get around Ton Sai is on foot. The beach and the main road act as the primary through fares for the area. It may take five minutes or less to cover the entire area. During heavy rains, the dirt road becomes muddy and treacherous.
Rock climbing is the primary draw for visitors, with Ton Sai offering as many routes as Rai Leh, and hosting a number of climbing schools and guiding companies, including:
Playing with fire -- Ton Sai could well be the world centre for fire tricks: light something on fire, twirl it in the air, that's the basic idea. A lot of climbers can be found on the beach during their rest days practicing.
There are several restaurants and bars on the beach and most bungalow operators have restaurants as well. Beware that many operations in Ton Sai are not electrified throughout the day meaning that unless they are careful with food storage you'll end up with a nasty case of food poisoning.
There are several bars on the beach, several of which (oddly enough) feature non-stop reggae music. A popular climber's hang out is Ton Sai Roof, at the east end of the beach, where the routes begin at the foot of Freedom bar.
All accommodation is set off of the beach and tends to be of the bamboo bungalow variety, and a little more rustic (and certainly more affordable though prices have more than tripled over the past five years) than at Rai Leh. Rubbish piles and noisy generators are common nuisances.
Contacting some of the bungalow operators for reservations can be difficult. Some of the climbing schools including Wee's (he updates the price list for the bungalows each year as well)  will book reservations for a flat fee.