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My kids spent a solid two hours turning the straight and curved pieces into a tunnel maze for their toy cars, which never happens. The interlocking holds tight enough that the whole thing doesn't collapse when they crawl through it.

The four different tube shapes click together in ways I didn't expect, so my son keeps rebuilding his maze into something taller. Water runs through the whole thing without leaking, which turned bath time into a engineering project.

The four different tube shapes click together way more securely than I expected, so the mazes don't fall apart when my son bumps the table. We've built towers, tunnels, even a little water run with them.