Like Osios David, this seemingly unprepossessing brick-and-stone church holds an astonishing treasure: well-preserved frescoes from the 14th century, the zenith of Thessaloniki's artistic excellence. You can pick out haloed St. Nikolaos himself, standing at the helm of the little boat he's guiding across stormy waters. The other frescoes, as is usual in such cycles, show scenes from the Old and New Testaments, as well as saints and prophets. Next to the church, part of its once-flourishing monastery with an attractive veranda has been restored, and makes visitors envy those lucky enough to live here. You may acquire a retinue of curious neighborhood children; most drift away in time, but some have hopes of sweets or even money and can be unpleasantly persistent.