The main attraction in Sai Yok National Park is Sai Yok Yai waterfall, which flows into the Kwai Noi River. The waterfall, an easy walk from the visitor center, is single tier and not nearly as spectacular as Erawan's. More unique are the bat caves, 2 km (1 mile) past the waterfall. They are the only place you can see the thumb-size Kitti's hog-nosed bat, the world's smallest mammal. Rent flashlights at the visitor center. Other caves worth visiting include Tham Wang Badan and Lawa Cave.
This part of the park has several options for accommodations, all without electricity. The private raft houses on the Kwai Noi River are the more scenic options. Those near the waterfall have inexpensive restaurants that are more pleasant than the food stalls near the visitor center.
Driving here from Bangkok or Kanchanaburi you'll pass Sai Yok Noi waterfall, also within the park's boundaries. Despite being taller than Sai Yok Yai, Sai Yok Noi has less water, but there's enough to swim in from June to November, when the area is often packed with Thai families on weekends.
Buses to Sai Yok Yai leave Kanchanaburi every 30 minutes from 6 am to 6:30 pm. If you're headed to Sai Yok Noi, buses leave Kanchanaburi every 30 minutes from 6 am to 5 pm. Either trip takes about two hours. Sai Yok Noi is also 2 km (1 mile) from Nam Tok Station, the terminus of the Death Railway. Trains leave Kanchanaburi each day at 5:52 am and 10:20 am. If you're driving to either waterfall from Bangkok or Kanchanaburi, take Road 323.