It has become aparant there is a new tunnel to build in Istaria. Its located just north of Aroth's Leap pad see pic below.


Its a massive task:
450 Bronze Jointings
500 Cedar Timbers
100 Dim Source
50 Dim Spheres
1200 Elm Braces!!!
2000 Elm Timber!!!
3000 Iron Sheetings!!!
300 Kenaf Bolt
600 Pale Spheres
1200 Sand Blocks!!!
400 Sand Keystones

Tunnel will change at 50% like the others, my guess is the tunnel will lead to portal and that will take us to new island somewhere.