(This is a little late, but...)
My "SafariSam" seed continues to provide strange and wonderful landscapes and features!
First, the "spires" I mentioned in my first post, which I now believe were the result of a chunk error (so, probably un-reproducible). Here are some close coordinates, in case you want to try and find them for yourself:
Here is a view from the base of the spires, which I have named "The Claws of Netherrack"
See the blue dot in this next picture? That there is the Void.
But wait, there's more!
While exploring the land around my home with a map, I stumbled across an underwater mineshaft! I was simply swimming through a lake, when I noticed that some clay appeared to be "floating" underwater. When I swam over to investigate, I was sucked down into a massive cavern, where zombies began attacking in the glow of a lava fall. Thankfully I had plenty of torches, and tools, so I decided to go exploring. Here is a picture of the "entrance", as seen from a ledge near the waterfall that dragged me here in the first place:
Apologies for the darkness of the image, it was nighttime. However, if you look carefully you'll see a creeper floating at the surface of the lake. It spawned in the cave.
Inside the mines, it is very twisty with lots of dead ends and gaps in the wall leading to additional caverns. I found a cave spider spawner; those things were a bitch to kill, and they were smart enough to hide in small gaps that I couldn't approach without getting bitten at least once. At least the treasure chest they guarded contained watermelon seeds!
I also may have found a creeper spawner *shudder*. I encountered a creeper in the tunnels, which thankfully exploded behind a wall. I found another creeper in a dark tunnel which I managed to kill without injury. When I turned the corner and found two MORE creepers, I turned around and walled off the hallway. I'll return some day, but I wasn't about to risk all of my loot without building a small base with a bed and chest.
More to come, maybe!