Find anything handy which would make good obstacles, E.g. chairs, tables, benches, skipping ropes, netting (for going under) or handy assault course if one happens to be near by 🙂 Then arrange the items in the most imaginative, safe but tricky and exhausting route possible. Also keep in mind the age of your players and what they skills they may or may not have.
Play as one big team or have smaller teams competing against each other. You can do this either by arranging it so that each team has the same course, eg doubling up obstacle or having some obstacles that two people can do at a time, or have timed trials with the fastest team completing the route winning.