On the Minecraft website, you used to be able to play a demo version. It was of a earlier build even when this was available. You were able to join multiplayer in this version. Because lava didn't have proper physics yet, it's spread more like a virus than a liquid. That got turned into a game mode where you had to build a home that could withstand the lava before the lava could get to you
Some people tried to be fancy about it. I just made a giant tower from bottom to the top. It's about a chunk in within. It was even more fun when I made it out of sand so I can watch it all turn to glass. The most enjoyable thing for me was the people who didn't finish their builds in time so they would rush into my build. It made me feel like I was running a hotel. Especially when they would build floors. I miss that gamemode a lot.