Considering the Hotel de Londres in Boulogne-sur-Mer?
A VT member wrote the following comment about visiting Boulogne-sur-Mer:
Cathedral by grets
There is a very interesting tour available of the crypt of the cathedral. Some of these are crypts of earlier churches discovered during construction of the cathedral in 1827. Some of these crypts date back as far as the 7th century and of interest is also pile of stone cannon balls from when Henry VIII besieged Boulogne in 1544.
The cathedral has the biggest dome in Europe after St Peter's in Rome.