Fey, fairies or faeries, dwell in the Fey-Realm and have a relationship with the elves. The Bound Bargainers (a faction of the elves) make gifts to and contracts with the fey; even the Bloodied King has contracts he must keep (including an annual delivery of human babies).
The Holt has many doors because of a clever agreement made by an elfmaid with a prince of the fey.