Towers

The old observatory in Copenhagen has a spiral corridor used as a racetrack.

These little castles each held thousands of pigeons.

Giant WWII fortresses that fired 8,000 rounds a minute, now home to thousands of pigeons.

Spain's stunning solar energy plant.

The tallest residential building in Africa is an unsettling Brutalist monolith.

Possibly the most beautiful carillon in the world, set atop Iron Mountain in Florida.

High atop the Eiffel Tower is a small apartment built exclusively to entertain the science elite and make the rest of Paris jealous.