Wooden Swingset Blue Prints Flooring For An Outdoor Wooden Swingset - Fort?

Flooring for an outdoor wooden swingset - fort? - wooden swingset blue prints

Looking for an idea that could be used for the amount of "substance" of a wooden swing. There is a staircase leading to a bridge, but the soil is full of mulch. I will be a 1 / 2 walls around takes all 4 sides and put a door a little scary for children.

What can I use it on the floor? I thought a wood base, but lost 3 "tall, and I fear that the bees nest can see below.

Other ideas? Outdoor tables or carpets? Each Webistan can recommend? Thank you!