This mod is currently in its very early alpha stages and as such does not have very much content.
The Barsoom mod adds Edgar Rice Burroughs Barsoom series into Minecraft.
I am currently reworking the entire mod from what I had originally. My plan is to go through each book adding content from them one by one. Once I add everything that I can from the first book I will then consider this mod to be in a fully playable release. I guess beta will be somewhere in the middle, I don't really know.
If you want to check it out there is a new dungeon that spawns underground in mesa biomes that will get you the item to travel to the Barsoom dimension. Or you can just grab the item from creative.