A "private den" refers to a personal space or room that is set apart from others. It is a secluded area where someone can have alone time or engage in their own activities without disturbance. Full definition
Over time, the crate will become your puppy's own private den — a place where it feels safe and secure. (petguide.com)
Place it in distant corner of the room, put in old towel or a blanket and your kitten will certainly appreciate its new private den. (snowyswan.com)
Additional features include a master bedroom with private den showcasing stunning views and «his and her» bathroom and closet. (sanctuaryoncamelback.com)