Sacred Haven of Debauchery

With 75% magic resistance (Breton ability + Atronach stone), a dragon could kill me in two fire attacks at most. On Legendary difficulty, yes. And yes, it was a regular dragon, not an elder or blood dragon. So, it's not that simple... Once you have 100% immunity and Ebony armor+, so it doesn't hurt so much, then it becomes manageable. But you have to survive until then, and you already need to start killing dragons...

75% magic resistance

Although it's not exactly 75% immunity, it works differently in practice. But still, it burned a lot.