Khagrachhari

A 100-metre natural cave inside the roughly 1,000-metre Alutila (Arbari) hill, with cold water flowing along its floor. It is pitch dark inside, so bring a torch; locals sell flambeaux. An easy day trip from Khagrachhari town.

A roughly 100-foot hill waterfall at Sapmara village, about 10-11 km from Khagrachhari town, reached by descending 235 steps. Wikipedia notes a small entry fee is charged from tourists.