Nest

there is exactly one way they fit.

nest five open rings — only one order lets all five settle

Five rings, five different sizes, and nothing marking where anything goes — the sizes themselves are the whole instruction, because only one of them is ever the biggest. Force the wrong pair together and it visibly refuses; there’s a small, real satisfaction in finding the one order everything actually accepts.

Concepts: order, nesting.

An interactive you play with one thumb, on Wundr.