An altar can be found inside the Clan Hall, in the small chapel in the south-eastern corner of the hall. Like most altars, this altar can be used to recharge prayer points.
Because the altar is located in the clan hall, access to the hall is required to use the altar. This can either be by being member of a clan or entering the hall as a guest.
When inside the chapel, several prayer-related sound effects play in the background. The altar does not seem to be dedicated to any particular god, regardless of which clan icons are set for the clan.