bolthole

A hole in an animal’s den, or through a wall or fence, used for escape or emergency exit, i.e., a hole the animal may bolt through.

Eragon: They may try to slip past us and escape Helgrind through the entrance we used. Saphira: They probably have a bolt-hole at ground level.

A hidden place of emergency refuge.

There was a guard at the front doors. He was smoking a cigarette; she'd seen the light from a great distance. They'd grown incautious in the absence of her continual raids, probably imagining she'd died of some viral infection alone in one of the countless caves ringing the forest. She'd seen their hunting parties canvassing the area, had prepared a few extra boltholes in case they found the one she'd shared with Yésica, but it hadn't proven necessary. Maybe they didn't really want to find her.

A second home, etc., where one can seek an escape or refuge from the stresses of everyday life.

a bolthole in the Dordogne

“We’ll find a home among the Fremen,” Paul said, “where your Missionaria Protectiva has bought us a bolt hole.” They’ve prepared a way for us in the desert, Jessica told herself. But how can he know of the Missionaria Protectiva?