Where does the Moon never get light?

The Moon's rotation axis is nearly perpendicular to the direction sunlight arrives from. That has a curious geometric consequence: in the polar regions the Sun never climbs high above the horizon, and the floors of the deepest craters are never oriented toward it. These are the permanently shadowed regions. They cover around 3% of the lunar south pole, and some crater floors have gone without a single direct solar photon for up to two billion years. In the same landscape the opposite happens just a few kilometers away: some peaks and crater rims stay lit almost continuously.

Perpetual darkness means perpetual cold, and cold turns those floors into traps: any volatile molecule that arrives there, carried by a comet or released from the ground itself, can stay locked in the regolith for eons instead of escaping into the vacuum. Hence the interest in water ice at the lunar poles, which would be both a record of the solar system's history and a resource for a future base. Mapping these zones isn't simple: since they don't reflect sunlight, they had to be measured by bouncing laser pulses off them from an orbiting probe to reconstruct their shape and terrain.

It's worth clearing up a common mix-up. The hemisphere we never see from Earth gets exactly as much sunlight as the near side: it has its own days and nights just like the other one, it simply never faces us because the Moon's rotation is tidally locked to its orbit. What truly never gets lit isn't an entire hemisphere, but small, scattered patches inside polar craters, the only places on the Moon where night never ends.