[Aegis]

Here's some ideas:
-Tunnels made of empty paper towel/toilet paper rolls.
-Cardboard boxes, or cut holes in them to make it more entertaining.
-Home-made obstacle courses made out of anything in the house, just don't let the hamster use it without your supervision.
-You could also try making a popsicle stick fort, but that might take more work (hamsters love it though because they can chew on the wood).
Hopefully this helps!
-Aegis