If you are trying to regarding:

: A central hub for music lovers featuring authentic performance costumes and library collections of the legendary bass singer. Alexander Nevsky Cathedral

It sounds like you're referencing a specific customer support ticket or interaction log. To help you effectively, I’ll need a bit more context.

While the specific "BJ" refers to the artist or event name (often shorthand for specific local entertainers or specialized workshops in the region), Sofia hosted several notable "first-time" and interactive events around this period:

:

: An open-air museum showcasing Roman ruins found during metro construction. Potential Contexts for Your Query Concerts/Events