A structure set aside for meetings, prayer and/or worship. Commonly sanctified in one manner or another. Usually part of a larger structure, though can exist on its own.
Alternate names: Oratory, Sanctuary
The first video game about Chapel was released on August 28, 1987.
Chapel is primarily Christian concept while oratory is essentially the same thing. Chapels are also sometimes called sanctuaries. Other religions don't seem to have synonyms for either oratories or chapels, though oratory is probably closer to what they actually mean (not always, predominance of silent prayer for example). For Christians the word oratory has fallen out of use in favor of chapel.
Private oratories and chapels have existed and still do, so neither can be considered more open than the other.
* Temple / church - the whole structure