hmm the tallest one that come in my mind is this one:
08:10 You see a sign.
You read: Outlook Tower
it It is located in thais and i remmeber Thais and I remember a quest( not sure wich which one ) that ask you to go to the higher place in thais Thais and was there probabily probably that why i tought I thought about it, checking in "map" on cyclopedia you can see the tower goes to the last level thing