Undercroft: A basement room in a church. Croft comes from a Dutch root meaning hill. A crypt is thus a room under the hill. In World of Warcraft, Undercroft is a crypt in Eastern Plaguelands inhabited by undead trolls.
Narthex: The entry to a church, the church lobby.
Post-Eucharistic Prayer: A prayer following the Eucharist (Holy Communion, the taking of bread and wine).
Nave: The large central part of a church, occupied by the congregation during services. Nave shares its etymology with navel (belly-button).
Eddie hated all churches, but found the Episcopal high-church tradition incomprehensible. The tinkling of the bells annoyed him, the clouds of incense choked him, and the secret code confused him: someone always seemed to be announcing the lectors' guild would meet in the undercroft, which should be entered via the narthex following the post-Eucharistic prayer in the nave.