I read that Baba lived in a mosque, but it doesn't sound like a typical one. What unusual activities took place there?

You are correct; the mosque where Sai Baba resided was highly unconventional. Chapter 7 of the Shri Sai Satcharitra details many activities that would be considered unusual for a traditional mosque. A sacred fire, known as a Dhuni, burned there day and night. The sounds of ringing bells and blowing conches, typically associated with Hindu temples, were heard in the mosque. Furthermore, offerings were made to the fire, constant bhajans (devotional songs) were sung, and food was distributed. The text also mentions the ritual washing of feet and worship taking place there. These practices, combined with the grinding of grain and a Tulsi Vrindavan in the assembly hall, made the mosque a unique spiritual center that blended elements of different faiths.