Belarus Station, the Moscow terminus for trains to/from Belarus (Minsk and Brest), Kaliningrad, Smolensk and international destinations including Vilnius, Warsaw, and Berlin, is around 3km north of the Akvarel Hotel.
By taxi
The drive to the Akvarel Hotel will take around 20 minutes in moderate traffic, and taxis should not cost more than $20 if you choose to negotiate with a driver on arrival. If you prefer, you can pre-order a transfer with a driver to meet your train here.
By metro
From Belorusskaya Metro Station (connected to the mainline station), travel south three stops on the dark-green line to Teatralnaya, which is around 300m from the Akvarel.