In Colorado’s Denver Federal Center, there’s a scientific storage facility where it’s always, always cold.

The National Ice Core Laboratory is the repository for samples of ice sheets collected in Greenland and Antarctica—miles of ice that contains information about the planet’s past and, in particular, the history of its climate.

The lab has more than 10 miles of ice cores. These opaque cylinders are divided into a smaller pieces and stored in aluminum-lined cardboard tubes. They’re kept in what’s essentially a very large, very cold warehouse, where the temperature is maintained at -36°C.

When researchers get permission to use part of a core, they can take their core to the adjoining research room, where they can slice out a portion of the ice and prepare for it to be sent to their own laboratories. This room is relatively warm—it’s kept at -24°C. Tours are limited and must be requested months in advance via a form on their website.