About 100 feet onto the sea ice (the section of ice that melts for a few months out of the year), next to one of the dive huts, is a large pistachio-green metal tube that is installed in the sea ice and extends about 10 or so feet under the ice.
The Ob Tube is available only when the sea ice is a sufficient thickness, and I expect it will probably come out in a few weeks. While it’s there, you and at least one other person (you cannot go alone for safety reasons) can go to the Ob Tube and take turns going inside and seeing the sea under the ice!
If you’re lucky, you will see seals, large fish, and even one of the divers. When I was there, I didn’t see any marine life larger than some small fish, but I did hear the occasional chirp and click from a seal.