On our server, there is a small village with a smaller underground village beneath it. One of the guys there decided to "expand" his house into a tower... and later on just started building a single block sky tower. As people ran out of resources, others joined in, and thinking we would hit the height cap soon, we kept building into the 900's.
Someone suggested this should get recorded, so I did.
Later on we passed 1000 blocks and the tower can be seen from REALLY far away. One plan is to store the pollution there.
Now the server has crashed, hopefully the tower was not the reason.
Disclaimer for admins: I have not participated in building the tower and forgot the names of those who did. I will remember for an engineering skill book (or better).