For me, this was a highlight of my time in Sri Lanka. I loved the tranquility at the top of the hill, a long with so much history. The fee is 1500 rupees, which is a bit high but well worth it. The trek up to the top is fine, 300 steps, there are water vendors halfway up. Remember to buy tickets from the bottom as they check tickets right at the top of the stairs but only sell them at the bottom!
The caves are fantastic, but it is one of these places where you need a guide. We got chatting to one and agreed on 400rupees. He gave us a really good tour for the best part of an hour. Showing us all the caves and giving thorough explanations of their history, talking about the kings as well as Buddhism in general. It was really engaging and he was capable of answering our questions with logical answers which was a treat! It is very peaceful at the top and well worth spending a but of time looking out at the view. We went during the heat of the day which worked out well for us as by the time we were leaving herds of tourists were entering the caves just snapping photos. Get a guide and learn about the place and it is truly interesting!