Mega Bloks Barbie® Build 'n Style Pool Party £20 @ Amazon
There are quite a few reviews of this Mega Bloks Barbie® buildable, multi-level pool and most of them are very positive.
Apparently this pool really holds water. As with all building blocks they have unlimited design and decoration possibilities and one of the reviewers says that they are compatible with Lego. I guess because there's not a huge amount that's actually buildable, in terms of bricks.
You can accessorize these with the included umbrellas, flowers, trees and more. It also comes with two figurines: Barbie and Ken.
This set is suitable for 4+
Thanks to djjonze at HUKD