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Splashing in cerulean pools under Erawan Falls is the highlight of this 550-sq-km park. Seven tiers of waterfall tumble through the forest, and bathing beneath these crystalline cascades is equally popular with locals and visitors. Reaching the first three tiers is easy; beyond here, walking shoes and some endurance are needed to complete the steep 2km hike (it's worth it to avoid the crowds in the first two pools). There are hourly buses from Kanchanaburi (50B, 1½ hours).
Bring a swimming costume (and cover-up T-shirt) but be aware you're sharing the bathing area with large, nibbling fish; monkeys have been known to snatch swimmers' belongings. Level four has a natural rock slide and level six usually has the fewest swimmers. Buggies (adult/child 30/15B) can transport people with limited mobility to the first level. Picnickers, be aware that you can't take food and drink to level three or beyond. Bottles of water are permitted but to prevent littering, visitors are asked to register bottles and leave a 20B deposit (which is returned when you show the bottle on your way back down).
Elsewhere in the park, Tham Phra That is a cave with a variety of shimmering limestone formations. Geologists find the caves of interest due to a clearly visible fault line. Contact the visitor centre before driving the 12km out there and a guide will meet you with paraffin lamps. There are several other fantastic caves in the park, but they're currently closed to the public.
The park was named for Erawan, the three-headed elephant of Hindu mythology, whom the top tier is thought to resemble. Mixed deciduous forest covers over 80 per cent of the park, but there's also dry evergreen and dry dipterocarp forest and big swathes of bamboo. Tigers, elephants, sambar deer, gibbons, red giant flying squirrels, king cobras and hornbills call the park home, but they don't frequent the waterfall area and you're unlikely to see them along the park's limited trails.
From the visitor centre, Mong Lay Dry Trail only takes an hour; for something more taxing, embark on the 5km Khao Hin Lan Pee Trail, a three-hour walk that takes you to the falls' fifth tier.
Park bungalows sleep between two to eight people. Tent hire is 150B to 300B; if you bring your own tent, there's a 30B fee.
From Kanchanaburi, buses (50B, 1½ hours) run hourly from 8am to 5pm and go right to the visitor centre. The last bus back to town is at 4pm, and on weekends it will be packed. Touts at the bus station will try to talk you into hiring a private driver instead of taking the bus, but this isn't necessary.