F3 Octagonal room. 

At the north end is
a circle symbol, gate to the Air Node.
 
T4 Nodes of Elemental Evil 1 2 3 4 5 6 7 8 9 10
T1-4 Temple of Elemental Evil 11 12 13 14 15 16 17 18 19 20
1eo 21 22 23 24 25 26 27 28 29 30