An ethereal glowing blue ocean cave in Croatia.

Formerly Yugoslavia's "forbidden island," this sleepy little city still holds the abandoned remains of military strongholds.

When Croatia became independent of Yugoslavia, the splintering governments left behind these concrete tunnels.

Two bulls enter. One leaves a champion—but neither loses its life.

This top-secret nuclear bunker hidden in a Bosnian mountain has been converted to a modern art exhibition space.

As the highest point in the Mid-Atlantic range this stratovolcano offers spectacular views.

This abandoned five-star hotel is now a five-star urban exploration destination.

Frank Lloyd Wright's most iconic home dangles over a Pennsylvania waterfall.