"Well, Viscount, there will be in my court-yard this evening
a good travelling britzka, with four post-horses, in which
one may rest as in a bed. M. Beauchamp, it holds four very
well, will you accompany us?"

A camper, 1830 style? equine powered motorhome?
From Tiscali, Dictionary of Difficult Words:
britzka
n. single-seated, four-wheeled, hooded Polish carriage