It is about 20 km from Belarus Station, the Moscow terminus for trains to/from Belarus (Minsk and Brest), Kaliningrad, Smolensk and international destinations including Vilnius, Warsaw, and Berlin, to the Aquarium Hotel.
By taxi
Depending on the time of day, the journey by taxi will take from 30 to 60 minutes, but should not cost more than $40. If you prefer, you can pre-order a transfer with a driver to meet your train here.
By metro
By metro, it is two stops counterclockwise on the brown circle line from Belorusskaya to Kievskaya. Then, take the dark-blue line from Kievskaya Metro Station and travel seven stops west to Myakinino, which is about five minutes' walk from the Aquarium Hotel.