Cluj has not too many green spots inside the city center so usually if people want to take a rest they rush over to the central park. Inside the Park there is a really interesting looking building which is abandoned right, now. Still 20 years after communism there are quite some abandoned buildings in Cluj (and Romania). Sometimes people do not have financial resources to renovate buildings or at least to conserve the current state but more often claims and property rights are still disputed. This occurred because after the revolution documents about property rights were destroyed or forged, allowing people with access to those documents to get rich at the expense of others.
Not far away from the abandoned building you can find a small pond and a restaurant (Chios). In the Summer this is a very popular spot also for weddings and and other kind of festivities. Of course you can also take a trip on the lake.