wheel nut . there are stripped nut removes available .
may not fit in there though . Or dive an old socket on thats smaller .
Vise grip . grinder, cold chisel and split it . or Might be able to turn it with a chisel to start the loosening process .
Arc Gouge is the easiest . Cutting torch . drill the stud out .
You may damage some thing in the process. It wont be easy .
Get or find a cheap 11mm socket (for 1/2 nut) or 10mm socket (for 7/16 nut). Hammer it on the stripped nut and it should back out. I keep extra lugs in my mag-tray all the time! Also, avoid using 12 point sockets They will strip the nuts quick! I prefer using a 6 point socket and a 12v dewalt impact. The 20v impacts just have too much torque for the fine thread. I know you didn't strip it to begin with, just suggestions to avoid this in the future, especially when you are in a situation where you are in a hurry to get to the grid. Good luck!