To get to the 'Grand Prize', I had to team up with someone else who also solved a riddle. The only options were Dot5, one of the best pvp-ers at the time, or JoeyC9, an old player who I knew nothing about. Naturally, I decided to work together with Joey.

Everything seemed to go well. He had access to the x-coordinate of the Grand Prize, while I knew the z-coordinate. We exchanged coordinates and started walking in the nether.

Then, out of nowhere, a player named 'bushd' shows up and starts crystalling me. I had no totems, crystals or blast protection gear at the time, so I disconnected and hoped JoeyC9 would defeat him. Logging back on sadly showed that this was all set up by Joey, and they had trapped my logout spot together, both swording me to death (see image). 
I lost the Grand Prize to JoeyC9 and bushd (Nyroc alt).

Luckily, they were kind enough to give me some of the items from the Prize afterwards, but some of the rarest items they kept for themselves.