Ok, so M chose a hex bug at the Liberty Science Center gift shop. Which was fine by me since a) it wasn't about space, b) it was small, c) it was much less expensive than most other stuff in the shop.
Next day we played with the hex bug (by the way, M chose the Nano, a bug that looks like and acts like a roach). First, we built a small enclosure for it with the blocks. Then we gradually expanded it and made it into a maze with several rooms. Along the way we figured that we had to reinforce the corners, otherwise the Nano was going to bang its head against them until a small crack would appear. Then just like a real roach, it'd squeese through and run away.
After building several versions of block mazes, we came up with a better idea. We cut a few "doors" in an empty cardboard box, turned it upside down trapping Hex underneath and tried to guess which door it'd run out of. Sometimes it'd run out of one door only to immediate run into a door next to it. That was a lot of fun.
Then I wrote numbers above each door. I kept it simple - 1,2,3. We counted out 10 beads for the Nano to eat. Depending on which door it'd run out of, we'd give him that exact number of beads. M especially loved this game.
Then I tried surrounding some of the exits with enclosures of different geometry - a rectangle, a triangle and a semi-circle, to see which ones the Nano would negotiate faster (find its way back to the door it came out of). This wasn't particularly exciting though since the Nano kept getting stuck in the corners where enclosures were taped to the walls.
I knew that we could buy a whole habitat for the Hex. It also doubles as a battle arena. But it looked very boring. Plus I didn't care to spend any more money and buy any more plastic stuff that we'd have to bring back with us. So instead we decided to create our own Nano habitat. M and I sat down, decided on various obstacles and general layout.
Then we raided our junk pile and recycling box to find tubes, wires, cardboard boxes, and plastic cups for a labyrinth. The end result was a bit unexpected. By the time we finished gluing down the last piece of the habitat, our Nano got lost. We couldn't find it anywhere and so ended up going to the store to buy a new one.