Caius Bar is located right in the Old Courts, just downstairs from the Hall. It's spacious, well-stocked and a great place to meet. The bar is well-designed with large booths, and many students go there for a drink after Hall in the evening.
By day, the Bar sells excellent coffee at good prices, and is a good alternative place to study. In exam term, it becomes an extra day-time revision venue, allowing you to enjoy cake and coffee as you cram.