I assume everyone had leaf cities in autumn, but also one family reunion we had an entire complicated underwater city of stone in the creek, and my big cousin G dropped a boulder on his foot trying to dam off part of the flow around it. This is the most important thing I remember about our family reunions: one time G dropped a boulder on his foot and his toe swelled up SO BIG but it wasn't broken okay it wasn't broken.

There was some wood involved in the underwater city, some leaves, but mostly stone, it stayed put better.