Lake Lohjanjarvi is the soft side of Lohja. Aurlahti, close to the centre, gives easy access to the water for swimming, boats, stand-up paddleboards and summer wandering.
This is not wilderness; it is a town lakefront, which is exactly its advantage if you are visiting without much time. Bring a towel in summer and treat it as the relaxed half of the day after the church or mine.