What is it that you must give before you can keep it?

You don't see me, but you count me with care. Too many of me, and your clothes have less to spare. The more you have of me, the more I increase your weight. What am I, this math problem on your dinner plate?

Now you see me, now you don't. Look away my location shifts. Take a picture, now my locations fixed. Effects instantaneous across any distance, two objects entangled, just as an instance. What properties describe these things and much more, it's a subject we can't fully explore.

Possibly the world’s most famous puzzle, invented by a Hungarian sculptor. The record for solving it is under three seconds; I still haven’t solved it in fifty two years.

Corridors snaking and doubling back in impossible configurations. If you escape earn a solid congratulations.