Very nice construction, I had the opportunity to watch one service. The interior follows traditional orthodox constructions and the exterior impress for its beauty.
This is a fine example of a Russian Orthodox onion-dome affair. Like most of Tallinn's centre, it is in a fine state of repair, and it contains some super art, especially icons.
The cathedral was under renovations when I was visiting Tallin, so I did not have the opportunity to go inside, but the outside was breathtaking!