While I was writing The Man who Broke the Bank at Monte Carlo I found it difficult at first to picture the layout of the Casino when Charles Wells went there in 1891-2. Then I discovered this plan in a book from 1912: it shows how the building was expanded over the years by adding new extensions.
The centrally-located Salle Schmit dating from 1898 is probably where Wells broke the bank at roulette on his first and second visits (in July-early August, and early November respectively. It was known at the time as the Salle Mauresque — ‘the Moorish Room’ — a reference to its Eastern décor). The Salle Garnier (shown here to the left of the Salle Schmit, and named after architect Charles Garnier) was principally used for the card game of trente-et-quarante, which Wells also played sometimes. The Salles Touzet — still further to the left — were begun in 1889, but were closed during both of Wells’ 1891 visits so that finishing touches could be applied to the decorations. They were re-opened immediately after the second of his forays.
(See The Man who Broke the Bank at Monte Carlo, especially pages 62-65, 83-86 and 231-235).