Pirates Lair on Tom Sawyer Island is a playground in Frontierland at Disneyland. While it's not the best, it is also recommended.
Disneyland's put a Pirate overlay on the classic playground for kids, where folks can run around and blow off steam built up from a morning of waiting in queues elsewhere in the park.
Note that the only way on or off of Tom Sawyer Island is by raft, and you can face a few minutes' wait to get back on busy days.
Walt Disney World