Nondescript from the outside, but far prettier within, thanks largely to its famous collection of antique clocks (don't be late now!), the Decameron is an old stalwart paladar that was always good, still is good and probably always will be good. The food is Cuban with international inflections. People rave about the savory tuna tart; ditto the sweet lemon tart.
On top of that there's a decent wine selection, powerful cocktails and the kitchen is sympathetic to vegetarians.