Caves, waterfalls and forest trails draw walkers to Sai Yok National Park (958 sq km), which never gets too crowded. The main sights are easily reached from the visitor centre, including the park's best known attraction, Nam Tok Sai Yok Yai, where a stream makes a short, graceful drop into Mae Nam Khwae Noi. More impressive than the waterfalls are the soaring shoreline cliffs that can be seen on a boat trip (400B, 45 minutes) from the suspension bridge.
Also here are a good nature trail; a bat cave with the very rare Kitti's hog-nosed bat, the world's smallest mammal at no more than 3cm; and some WWII Death Railway relics – the rail line passed through what is now the park.
You can stay within the park in old bungalows, at a campground (tent hire 225B, per person with own tent)30B or in basic – but fun – raft resorts.
Sai Yok National Park lies along the highway between Kanchanaburi and Thong Pha Phum and buses (fan/AC 55/75B, 1½ hours, every 30 to 45 minutes) between these destinations will stop at the park turnoff. A túk-túk driver can take you the last 3.5km for 30B per person, or 50B for one person. The visitor centre will call for a túk-túk when you're leaving the park.