This is one of the official DLCs that you can get in Oblivion. I noticed I never actually talked about the DLCs that you can get for Oblivion. Basically after you load Oblivion with this installed, you will receive the deed to the Frostcrag Spire and the key. Once you read the letter, you find out that you are the sole heir and successor of your recently deceased long-lost relative.
The spire is located on the Jerall Mountains and east of the city of Bruma. You will get a map marker for its location so you don’t have to worry about figuring out where it is. Upon arriving, you see a frost atronach’s hand sticking out in what appears to be the only room in the Spire. You have to read the book that is on the hand, which gives you an update to say if you want the full facilities of the Spire, you have to purchase it from the relative’s friend who will found in the Mystic Emporium within the Imperial City.
Once you buy everything, the wall will move revealing the interior of the spire. You use portals to move up to the living quarters or the vault. It also provides you with an altar to create a permanent atronach familiar and the two altars; spell-making and enchanting so if you aren’t a member of the mages guild, you can use the altars within the spire. However, you have to purchase the mega-tallow candles before you can use the altars.
Your living quarters contains an alchemy station, where if you get close to it will give you a temporary boost to your alchemy by 15 points. Your living quarters also has an alchemy garden so you can collect your ingredients with ease. There is also another portal (inside the bedroom area) that leads to the top of the spire, so you can admire the views from your new home.
You also have a door that leads to outside, where there is a platform with portals going to each of the major guild halls. Except for Kvatch for obvious reasons. In your vault, you have guardian imps everywhere to make sure your treasures are safe. There is plenty of storage space in the vault area, even a little area sectioned off for your wine collection.
However, if you are not satisfied with Frostcrag, there are 2 mods that revamp Frostcrag Spire. One called Frostcrag reborn (which I believe was not completed) and This Mortal Crag. Both completely change Frostcrag and give it an overall quest line to explore new areas.