Where was Manwë?

I believe it was mentioned that Manwë, as long as they lived in Aman, was always in his halls on the top of the Taniquetil. That he never came down and would not come down until Melkor returns.
Which made me wonder: Has any elf ever seen Manwë?
Could any Elf survive the ascent to his halls on the Taniquetil? Maybe that's a bit influenced on my knowledge how long people can survive on the Mount Everest. But was that ever addressed in the texts?
But my biggest problem is the Circle of Doom. The Máhanaxar. It was definitely not on the Taniquetil. So was Manwë never physically present during any of the big decisions, including Melkor sentenced to three ages of imprisonment?
Somehow I have troubles believing that, but it seems like it.