Nog- Well sure if we go strictly by the word "fortified" then places become better options, but the word is "dangerous", not "fortified". Let's not get side-tracked on what is by far the least synonymous of the secondary words offered.
(Unless you are particularly wishing to, in which case I can let it drag out longer.)
Besides, Sauron still trumps Barad-Dur and Minas Morgul because they are only dangerous because of him. When Sauron perishes, so perishes the foundations of Barad-Dur, so that one is quite plain. And Minas Morgul is only named so (rather than Minas Ithil) thanks to Sauron's ownership, so again that seems plain.
And the House of Ransom would likely prove a dangerous place to go during the years of Turin's stay, but no one ever did go there because the way was not known. And never mind the countless years before that when no one went there. When unwelcome guests finally did show up, they showed up in force and slaughtered the folk there, so it only proved dangerous to the dwellers, and only that one time. Where as the Misty Mts were frequently traversed and often with disastrous results (wolves, orcs, weather, etc.). So quantitatively it's proven more dangerous.
I don't particularly want to toss palantirs so early, but I can't help it next to Silmarils. Not only do they scorch anything that isn't pure, but the wreaked such terrible damage in the world (Morgoth's lust for them drove him, Feanor guarded them so jealously, the Valar's request for them pushed Feanor over the brink, Beren & Luthien's adventure, Carcharoth, Feanor's sons destroying Doriath & the sea-side colony, etc.
And then there's obviously Sauron- the largest destructive force in the world during the second and third ages, and one of the tops of the first. I mean- he's the one that created/finished orcs and trolls, and look at the many results of that. Plus werewolves at Tol-In-Gaurhoth of course, and slaughtering Elves and Men in the second age halted only by Numenor- which he eventually destroyed through trickery. And need we recap the War of the Ring?
Sauron and the Silmarils seem to be in their own category. One simply wants nothing to do with them, and survival rate isn't high when one gets in close proximity... and Misty is sort of my heart's fond choice (memories from imagining them first time reading Hobbit & LotR).