>>9909474Mount Shasta, but unless you have special equipment(ie The Key), you aren't getting through the holofield.
You can roll the die and see if you have enough Atlantean blood to get through without a key, but then you face a 3km freefall to deal with before you reach the entrance tunnel, which is guarded by AI. You'll be molecular seperated if you don't have atlantean dna, and the process is instantaneous so at least its a quick and painless death.
Supposedly there are a few lava tunnels with non-holofield physical 'entrances', but they are speculated to be exit-only as a type of emergency escape tunnel.
The maidu had limited contact with atlanteans moving in and out of Shashta, but enough for it to be passed down in their oral tradition.
