The Museum of Volyn Icon is a small but serious collection of sacred art from Volyn, with icons, crosses, sculpture, and liturgical objects from local churches. It gives Lutsk a regional context beyond the castle, especially for travelers interested in Orthodox art and the religious history of western Ukraine.
The museum is not flashy, and labels may be limited, but the collection is strong enough to justify the walk from the old town. Pair it with the castle museums rather than treating it as a quick photo stop.