Batu Caves are famous for being a Hindu shrine where over a million devotees ascend to during the annual festival of Thaipusam, which typically falls in January or February.
In order to reach the limestone caves, you have to climb 272 steps. It's best to take it easy and stop a couple of times along the way. On my way up, I passed two people, on different levels, who had passed out from exhaustion. Luckily, there were first-aiders around to assist.
Oh, and beware of the monkeys. They're conniving creatures that try to steal anything loose hanging from your body.
Incidentally, at the bottom of the steps is a giant golden statue of Lord Murugan. It's the tallest statue in Malaysia.
(This photo was taken one day before Thaipusam—hence, the crowds.)