The Cloister of Lightning is the Wierd Japanese Symbols on Boyahda tree 2. the Pos is j-12... you go though neat looking water fall at I-11
Other things to Note...
You enter from Boyahda tree1 - 1 or 2
the only way to get to the Second MAP(2) is through pasage marked A.
The 3rd map is Reach by dropping down the falls at map 2 point C. For there you can head north to what I assume is the Dragons aery... I dont know ... I died some Elder Goobue hit me for 483...ouchie.