In my cognitive science and philosophy of mind course, I often explain that computations can be realized in all sorts of ways. There is no reason why a computer has to be electrical. Computations used to be done by hand, and the word "computer" was first used to refer to someone whose job is to do tedious computations such as calculating trigonometry tables. There are now also biological computers using DNA, but here is a computer made of lego that implements Charles Babbage’s famous difference engine. It can calculate 2nd or 3rd order polynomials to 3 or 4 digits.
Lego difference engine – http://acarol.woz.org/
Here is a set of logic gates made from lego : http://goldfish.ikaruga.co.uk/logic.html