I'm afraid that I don't remember the exact spot where I used Vanish.
What I did do was go to various likely-looking places (only a small
line of trees separating two open spaces) and cast Vanish once at each
of those places until I found somehwere that it worked.
I think that I had to Vanish myself into the "leprechaun area" first
and then work my way over to the Lost Sea (again with more Vanish spells).
However, once you're there, cast a Create Portal and you're all set. (Not
all Cet though, that would get you pursued by hundreds of Mavin-wielding
would be "Chosen Ones"!

)
------------------
Bear
"No matter where you go, there you are. " - B. Banzai