The Varna Aquarium is one of the oldest aquariums in Bulgaria, founded in 1912, and focuses specifically on Black Sea marine life. This is the interesting part: the Black Sea is an unusual body of water — below about 150 metres it is almost completely anoxic, meaning it lacks the oxygen to support most life, and the diversity in the upper layers is distinctive. The aquarium's tanks display the fish, invertebrates, and marine plants that actually live in the sea a few hundred metres from the front door.
The facility is not large — this isn't a Barcelona or Genoa-style aquarium with whale sharks and vast tanks. But it's well-curated and the focus on a single sea gives it a coherence that many larger aquariums lack. Good for children and for anyone curious about what exactly lives in the water they're swimming in. Located near the Naval Museum in the lower part of the Sea Garden.