I bought the 6676 cool dude in his inflatable raft, plus the 6670 Water Playground. The 6669 Waterpark was too expensive for me at the moment though, so (after a lot of complaints from Cool Raft Dude, about how he had to sit in waterfalls or ponds and how he didn't like that) I bought a secondhand 5433 Children's Pool with Whale Fountain instead. It fits together quite well:
See on that photo, though, the dark blue supports for the platform (far right side) ... there are three of them, and the fourth side is supported by the green shower. Very nice, but I wanted to move the Water Playground off from its base. Seemingly impossible unless one has another unique-sized dark blue support. And they are
not available form Direct Parts!
Grrrrr.
Nonetheless, with a few adjustments and much patience, it
is possible to turn the Water Playground into something else.
I don't know what on earth this posts-with-slits-in and things-to-stick-in-the-slits building method is/could be called, but I do love it.