17 Secret Video Game Bosses You Need To Beat Before You Die
12. The Elder Scrolls V: Skyrim - Karstaag
How you get there: Before you do anything in an attempt to find Karstaag, you'll need to have Skyrim's Dragonborn DLC installed. With that financial obstacle out of the way, you can start the hunt for Skyrim's secret, and undisputed, hardest boss.
You won't be able to rely on your quest log as a crutch either, Karstaag's quest is unmarked. After you find the long-dead giant's skull resting on a shoddy plinth in the Glacial Cave, you can take it to Castle Karstaag and put it on his throne, where it belongs.
Why you need to beat them: The ghostly remnants of Karstaag represent the biggest challenge in the entirety of Skyrim. The lumbering spirit makes Alduin look like a plush child's toy in comparison, and he's only a bloody ghost too. If you're ultimately up to the challenge and can deal with everything Karstaag throws at you - including almost endless amounts of Ice Wraiths - you're richly rewarded with the ability to summon him.
There's a catch though. Due to how ridiculously overpowered the spell is, the ability to summon Karstaag can only be used three times across your entire playtime. Use it wisely.