There was a volcano once at Sirigiya. It eroded away long ago but a 350m tall basalt plug that was the magma chamber still stands. Naturally a Buddhist meditation place was built on top sometime around the 5th century, and now there's tourists crawling all over it. Fortunately, I was there before the crowds arrived.
There are stairs leading up part of the way; the rest is steel stairs, walkways, and a pair of spiral staircases that allow a nice view of the sheer rock face below your feet. Halfway up are some amazingly well-preserved paintings, plus ancient and modern graffiti on a wall alongside the paintings. Plus ça change...
The view from the top is stunning. Much of this part of Sri Lanka is a national park, and there are forests, lakes, and mountains all around with little evidence of civilization - with the exception of a huge shiny white Buddha in the middle of the forest.