List of 'Pre-Oblivion Portal' Locations?

[Vezera]

I understand that the Oblivion Portals start appearing after Kvatch and spawn randomly throughout the map. I also understand that there's some locations on the map that are forever changed once that starts happening. Is there a list of said locations to look at to maybe visit these areas a lot of people may possibly never see?

[Wai]

I cannot give you a complete list, but there are two which I know of which may affect your game.

The Wayshrine of Kynareth:
Fast travel to Castle Skingrad, and cross the bridge and head east. The Wayshrine is on top of a small hill. This Wayshrine can still be used after the portal has opened).

The Wayshrine of Mara:
Fast travel to Horse Whisperer Stables outside Anvil, and head west-northwest. I am pretty sure this Wayshrine cannot be used after the portal has opened).

There are other Kynareth and Mara Wayshrines on the map, but, these are the easiest to find if you are doing the pilgrimage quest.

https://en.uesp.net/wiki/Oblivion:Oblivion_Gates

The above link is a list of all places where Portals may appear. But, it does not say if the area contains any important structure which may be damaged by the Portal.

[Lobo de hielo]

There are 20 fixed places, 10 of which appear after Kvatch/ Find the Heir quest.
See https://en.uesp.net/wiki/Oblivion:Oblivion_Gates for more info.