The Consilium stronghold and meeting place is in a high-rise hotel called the Conwell. The building is actually owned by the Consilium and the top two floors are for the mages of the city exclusively. There is a catering and ballroom setup on part of the top floor used for the main gatherings of the region’s mages. The rest of the hotel is run as a regular business, generating income for the Consilium. Council members have suites set aside as one of the benefits of their position.
Mystically, there is a small Hallow on the top floor, at the opposite end from the ballroom. There are magical wards to prevent unauthorized access by Sleepers, as well as mundane key-card swipers only given to Consilium officers (Councilors, Heralds, Sentinels, etc).
The Athenaeum is just outside Philadelphia city limits in Montgomery county along PA route 63. A new development gave the Mysterium the opportunity to move to a new location they could control better than the warehouse they were using. Once the house was built, they created more space in the basement to house the collection of lore and objects. This is also where the Mysterium Caucuses are held once a month.
The house itself is large but somewhat unassuming, since all the other houses in the development look almost the same. Magic has been used to reinforce this feeling, and most Sleepers overlook the building as nothing special. Many other wards have been put in place to keep out, or at least severely slow down, unwanted visitors. The mundane security measures take care of the rest.