Cronvangr Cave is a dungeon in The Elder Scrolls V: Skyrim
This is a cave found South of Windhelm. When you go inside and around the first corner you will encounter a Frostbite Spider that is pacing ahead of you. It is very easy to sneak up on this one. The thing is, attacking this spider will aggravate the other 3-6 spiders that are nearby. Stay hidden and you can easily pick them off as they advance.
Head down the slope to the lower portion of this cave. There is a hidden door with a button in the Northern side of this lowered area. Move forward carefully as there is a pressure plate flame spout trap in front of you. In the room in front of you there is a Vampire that you will need to deal with. Be careful as there is also a nearby corpse that they can reanimate and send after you. There is also a Vampire's Thrall in the room as well.
After you have dealt with them then head on up toward the house in the back part of the room. Go up either side using the slope. Approach the house carefully. Inside you will find a Vampire Fledgling and another Vampire. Defeat them and you can search the house. In you will find 2 unowned beds that you can rest in. You will find a coin purse sitting one of the bookshelves. On the other you can find 3 Fear Poisons. In the Western part of the house you will find an empty Strongbox and a copy of the skill book The Locked Room sitting on a table with a lot of bloody parts. Behind the house is an Arcane Enchanter that you can use. To the right of that is a locked chest (Adept level). Opposite the Enchanter, to the South, you will find an Alchemy Lab that you can use as well. This area is a dead end otherwise.
If you head to the South, this leads to a web-filled corridor. To the left of the entrace of this area is a Iron Ore Vein. At the far end of it you will encounter a Larger Frostbite Spider with a few Frostbite Spiders backing it up. This is a tall room with a downward spiraling trail. There are more Frostbite Spiders on the trail as you make your way down. Be sure to check along the sides for mushrooms as well.
When you get to the bottom, dive into the water. At the bottom of the pool you will find a chest with a potion and some other goods. After that, check the surface for any spiders that fell into it. Then head out through the nearby doorway to the East. This will lead to the deeper Cronvangr Broodlair