Based on this bulletpoint from the allowed topics:
- Which tools, materials, and best practices for home improvement task.
I'm looking for advice on dealing with our playset. Specifically the area beneath it that they usually recommend being a sandbox. We don't want a sandbox. However, since we haven't done anything with it yet, the thing ended up being a mud pit with some interesting weeds growing.

So my questions are:
- What materials and best practices can I use to make the area a usable "indoor" space for the kids with a flooring of some kind and maybe even a door or gate?
- What do I need to do to make sure the flooring is weatherproof and won't become muddy or allow weeds/grass to eventually poke through?
- Any advice on making sure critters, bugs, spiders, hornets, etc. don't decide to take up residence inside?