I may have reached the 'kill screen'?
I was building this tower for maybe 4 hours. I called it "The Tower of Babula".
No clue how tall it was because it wouldn't let me do anything but reload the page. At a very conservative estimate this one's Castle Height is at least 1500. My run before this one (only 1 block wide for most of it) lasted ~30 minutes & reached 534.
Previous run's stats:
