Barad-Dûr was built upon the end of a long southern spur of the Ered Lithui in the northern part of the Plateau of Gorgoroth. It stood about 30 miles east of Mount Doom and about 100 miles southeast of the Black Gate. There was both a road leading north to the Black Gate and Sauron's road to the Sammath Naur leading west to Mount Doom. Latter ran from the Dark Tower's western gate over a deep abyss, the plain and around the mountain to the dark entrance of the Chambers of Fire.
Source : Tolkiengateway.net

I'm kinda bit disappointed with the height limit, oh well.