The Citadel is a homeless shelter in St Paul, the new location is not far from downtown, can't remember the previous location. Lowertown is a section of downtown St Paul. Also in St Paul/Lowertown-ish is House of Mercy, a church which attracts mostly young people and the church band is made up of many locally famous alt-country rockers, lots of people go for the music and buy the cds.

Alternatively, given the strong religious theme of this verse, and especially considering that Holly was "checking out the 530 folk mass," it seems possible that the Citadel mentioned is in fact the Citadel Hope and Worship Center church in Minneapolis, MN.

St Paul Citadel

Citadel of Hope Worship Center

from Multitude Of Casualties