Odesa Catacombs, Geological monument in Odesa Oblast, Ukraine.

The Odesa Catacombs are an underground network of passages stretching over 2,500 kilometers and reaching 60 meters below sea level. The system consists of three separate levels connected by narrow corridors and larger chambers.

In the 19th century these passages formed through limestone quarrying for city construction. During World War II Soviet partisans used the tunnels as hideouts and communication routes.

The Museum of Partisan Glory in Nerubaiske displays objects and records from the time when resistance fighters used these passages as shelter. Visitors see everyday items, hand-drawn maps and weapons that document life underground during the occupation.

Visitors may enter the tunnels only with experienced guides, as the sprawling network includes over 1,000 entrances and it is easy to get lost inside. Warm clothing is recommended because the temperature inside remains cool throughout the year.

The quarries' karst deposits have yielded Pliocene mammal fossils from around 3.5 million years ago, among them the camel Paracamelus alexejevi, the elephant relative Anancus arvernensis, the three-toed horse Hipparion and the sabertooth Homotherium, one of the oldest records of that cat.