Camera obscura

You need a mirror, a surface in a dark room - and a bright day. The light hitting the mirror shines down onto your surface, and you see what's happening outside. Magic! The whole wide world is brought onto your tabletop...

Usually camera obscuras are situated at the top of towers or other buildings. I've visited them in Edinburgh, Eger (Hungary), and Bristol - and with the help of this directory hope to visit others - there's one at Greenwich, not far away.

This one was built in 1990 for the Gateshead Garden Festival and has since found a permanent home -
Chris Drury's "Cloud Chambers" are camera obscuras, for instance "Cloud Chamber for the Trees and Sky" in North Carolina -This is what it looks like inside - trees and sky -
In this video of "Cloud Pool" being installed in Nevada, he says "It's an object, and it's an experience".
There's another at the Eden Project in Cornwall.