Varousi is the old Turkish quarter of Trikala, clustered at the base of the castle hill. It's the most atmospheric part of the city — a dense cluster of old stone houses, some dating from the Ottoman period, connected by narrow lanes that have been gradually restored and repopulated with cafes, wine bars, and small restaurants. The neighbourhood has been carefully preserved rather than heavily developed, which gives it an unhurried character.
Walking through Varousi is the best single thing to do in Trikala. The lanes wind up toward the castle walls, and the conversion of old stone houses into simple but appealing places to eat and drink has been done with enough care that the area feels genuine rather than constructed. Come in the evening when locals come out for their volta (evening stroll) and the cafe tables fill up.