Sivas Grand Mosque is one of the city's older Seljuk monuments, built in the late 12th century with a minaret added in the early 13th. It is plainer than the medreses, but that restraint is part of its value.
Visit it as a counterpoint to the carved portals nearby. The mosque shows the older, more sober layer of Seljuk Sivas before the showier medrese facades took over the centre.