When this campanile—of the church of San Martino,
on Burano—was constructed, they apparently didn't allow
for the marshy land. Oops, and yet it still stands.
They're working on the belltower of San Marco, in Venice
(which doesn't even look like it's leaning and we're
still allowed to go up into it), so I have to wonder
if there are any plans to "straighten" this one.
[You can see more "construction" here.]