Describe the house, the man who opens the door, and General Zaroff?

The house is a grand gothic-like castle, 

The dining room to which Ivan conducted him was in many ways remarkable.
There was a medieval magnificence about it; it suggested a baronial hall
of feudal times with its oaken panels, its high ceiling, its vast
refectory tables where twoscore men could sit down to eat.

Zaroff is a handsome refined aristocratic man of middle age. 

Rainsford's first impression was that the man was singularly handsome;
his second was that there was an original, almost bizarre quality about
the general's face. He was a tall man past middle age, for his hair was
a vivid white; but his thick eyebrows and pointed military mustache were
as black as the night from which Rainsford had come.

Ivan is a hulking Russian man with a long beard, 

The first thing Rainsford's eyes discerned was the largest man Rainsford had
ever seen--a gigantic creature, solidly made and black bearded to the
waist.