ericbnc wrote:

How is Odessa?

Russian forces continued to target Odesa with cruise missile strikes and conduct false-flag attacks in Transnistria over the past several days.
Ukraine’s Operational Command South reported that Russian aircraft launched four cruise missiles at Odesa Oblast (Oblast = engl. Region) on May 7 and two missiles late on May 6 to exert “psychological pressure” on civilians (ISW May 7, 6:45 pm ET).

Btw. Zmiinyi (Snake) Island is far far away.

On the way E to W from e.g. Mariupol to Odessa is the town Mykolaiv (Mykolajiw), very difficult to cross the big river in this region.
RU tried to cross the river since a long time, lots of counterattacks, ISW Mykolaiv map May 7.

Odessa has 2.500 km Catacombs (under the Mariupol Steel Plant are 25 km and none in the town),
see Wiki: Odessa Catacombs
I am not a military specialist, but tunnel systems in this dimension would be perhaps difficult to capture.