Plasticine..
Used to spend an age constructing intricate 'spaceships' including the control panels and occupants then 'crashing' them and doing an autopsy of sorts.
I should have had a therapist, probably still need one now...
lol... building stuff, then destroying it... I used to do that IRL 3D when I was a kid, lol... lots of stuff got built from the ground up... only to be destroyed later.. thanks Rox for making me relive that for a bit!