Sorry! These posts are out of sync! Because our flight was a night flight we took our time in getting to the airport and took a diversion to the science museum in Tsukuba. There was a lot of hands on stuff to do, plenty of experiments and pretty much everything had an English explanation too!
Surprisingly it wasn't very busy. We spent a couple of hours in there which was enough, it wasn't big enough for an all day event.
I imagine it gets used a lot for school trips and looked like upstairs they had group talks etc. Worth a visit if you are in the area.
Once we were done we headed off to the airport.