I got the idea from my daughter's gymnastics class where they set up an obstacle course for part of the class and the kids love it. We all build tents or forts with our kids, why not set up an obstacle course? It takes about the same amount of time, and depending on their personality, can keep them entertained for much longer than a fort.
We started the course with a balance beam made out of painter's tape. On the balance beam, they can practice walking forward, backward, sideways, hopping, or whatever you can come up with.
Next obstacle was to climb over the ottoman/coffee table. Use what you have,but try to find things for the kids to climb over and crawl under.
After climbing over the ottoman/coffee table, they had to crawl through the tunnel (blankets draped over the kitchen table).
From there, they went back toward the start and had to jump in the boxes (again, made of painter's tape), two feet where there are two boxes and one foot where there is one box. After the boxes, I simply put a start line and a finish line for the kids to see how far they can jump.
Then they were back at the beginning and could start all over again. I recommend doing this with at least 2 kids as they seem to be better entertained by this in a group. Also, playing some music makes it more fun :)
I hope you enjoy trying this with your kids.