One of the Cossacks galloped ahead, as soon as they arrived at the station where they changed horses, and had fresh ones in readiness at the next post house.

The Cossacks themselves were changed at every other station, fresh relays from the men stationed there taking their place.
Excellent meals were served three times a day, and each night a comfortable bed was provided, at the last post house where they stopped.
The officer was a pleasant fellow, but he spoke nothing except Russian, and, although Charlie fancied he understood him to some extent when he spoke to him in Polish, he shook his head and gave no answers in that language.
Late in the evening of the third day, they arrived at Notteburg.
The building at which the carriage stopped was of considerable size.

It stood in the heart of the town, and had no outward appearance of a prison.

It was apparently at a side entrance at which they stopped.

On the officer knocking at the door, it was opened by two Cossacks, who, after exchanging a few words in Russian with the officer, led Charlie along a passage and up a narrow staircase, which led into a somewhat spacious corridor.