You can spot lots of terrapins (some small, some very big) swimming around this pond or chilling on the rocks.
One time, I saw this guy hanging out there too.
If you are coming from the Tsuen Wan line, take exit C1 and you'll be just across the road from it. If you are coming from the West Rail Line, you can come out directly into the park.
Looking for a lunch spot? I'm a fan of Wolf Den, which is adjacent to the park. A nice spot, with outdoor seating to have a coffee and some lunch.