The Bolthole is the refuge and safehouse of an Unchained, similar in function to the Haven of a vampire. The bolthole is part of the Infrastructure that maintains the demon's Cover (though the demon can access it no matter what Cover she wears), which means it doesn't exist entirely in the physical world. It has an entrance anchored to a specific point in the real world, but the location itself exists outside three-dimensional space. Boltholes are neither spacious nor luxurious - at best, they're a dingy, dimly-lit windowless space about the size of a one bedroom apartment with enough space to house three or four people, but have other benefits.
Within a Bolthole, time does not pass. People do not get hungry, age or need to sleep. This atmosphere of timelessness can be startling for mortals, who are likely to suffer a Breaking Point after a specific amount of time spent in a bolthole. They are nearly impossible to find without the cooperation of the Demon or a person who knows of the existence of the bolthole, and are warded against intrusions from Angels.