The Lutheran Church of the Holy Trinity is the oldest surviving building in Mikołajki and the architectural centrepiece of the small historic quarter. The present structure dates from the 18th century, built on foundations that reflect the town's Protestant heritage as part of the historically German-speaking Masurian region. The simple whitewashed exterior is typical of Masurian Lutheran churches; the interior is modest but well-maintained.
The church sits on a slight rise above the waterfront, and its tower is visible from most of the lake. It is still an active Lutheran congregation — one of the few remaining in a region that was predominantly Protestant until the post-war population transfers of 1945.