Here's a picture of my 'play area' for my ND's:
They have two wooden spools with a 2x10 going between them as a bridge and a ramp going up to one of them and a smaller spool just to jump onto. I have three tires buried in the ground next to each other that they can jump up on. I have a rabbit hutch that they love to be on top of and two dog igloo houses that they love to jump up onto also. I have recently added several straw bales making a tunnel into their dog igloo house and they spend a lot of time on those bales.

They have two wooden spools with a 2x10 going between them as a bridge and a ramp going up to one of them and a smaller spool just to jump onto. I have three tires buried in the ground next to each other that they can jump up on. I have a rabbit hutch that they love to be on top of and two dog igloo houses that they love to jump up onto also. I have recently added several straw bales making a tunnel into their dog igloo house and they spend a lot of time on those bales.