Ukraine seems to have three main Christian churches: the Orthodox Church of Ukraine (formerly the Russian Orthodox church); Ukranian Greek Catholic church and the Roman Catholic church. Each of these groups has spent centuries building spectacular churches in Ukraine. Each has a cathedral in Odessa. My guess is that there could have been some competition that resulted in three beautiful churches. In looking at these photos remember that the Russian Communists completely opposed religion, particularly in the early 20th century when churches were closed.
The Greek Ukrainian Orthodox Church:
The Greek cathedral banned the taking of photos but I found this one online:
Russian Orthodox (Eastern) Cathedral:
The most spectacular church I found is not a cathedral and I don’t know its name. Below and at the top of this post are two inadequate photos. I believe it is Eastern Orthodox.
And on my last day in Odessa I found the Mosque:
There’s a synagogue but I didn’t find it.
Want to know more? Here’s a link to an informative Wikipedia article about the history of churches in Ukraine. The section beginning with the heading “Twentieth and Twenty-first Centuries” is most pertinent, giving the history of the Soviets’ opposition to religion. https://en.wikipedia.org/wiki/History_of_Christianity_in_Ukraine