I climbed a lot of stairs in France, especially spiral staircases. The Arc de Triomphe and Notre Dame Cathedral come to mind, as these structures were build before elevators were commonplace.
All I can say about spiral staircases is I'm glad I've been cycling a lot this year: my legs held up, no problem (the same can't be said of my feet).
Of course, putting in the effort to climb all of those stairs has its rewards. The views from up top are almost certainly worth it.
Coming down is another matter.