Which theater does Dunny seek out that is significant to his past?

Dunny seeks out the Royal Alexandra Theatre because it holds significant memories related to his childhood and his relationship with the arts, particularly his connection to the performance of the past. This theater serves as a symbol of Dunny's journey and his ongoing search for understanding himself and his place in the world. It embodies key moments in his life, reflecting his growth and development throughout the novel. The Royal Alexandra Theatre is not merely a physical location for Dunny, but a representation of the intertwining of personal history with the cultural landscape of his upbringing.

The other options, while they are notable theaters, do not have the same direct connection to Dunny's formative experiences and the themes of memory and self-discovery that are central to "Fifth Business."