This short video was put together by Golem Dragon after a request from a fellow Ultima Dragon; it shows how to take advantage of the Disk Swap Map Exploit in Ultima 4.
This was a popular exploit in its day, and could be used to collect gold very quickly, enabling players to afford to buy items to beef up their characters. Golem initially showcased the exploit in a live stream, and subsequently released it on YouTube so that it was easily available.