I like the majestic mosaic which is Bitcoin. It brings together many fascinating concepts is a way which inspires awe:

Proof of work

Byzantine Generals’ Problem

P2P, self-custody

Distribution over time, the halving

Difficulty adjustment

The disappearance of the founder

Tripe entry ledger

Difficulty adjustment

An interesting social layer: toxicity, sovereignty, free-market economics, distrust of the state, aware of incentive structures, personal responsibility