The Mana World Forums

A passage between towns would need to be really huge, considering the towns are on different continents....
http://wiki.themanaworld.org/index.php/Geography
So if you want to create a connection between towns that you can walk, you'd have to explain it with some kind of magic teleportation anyway, and we already have teleport between places.
Some quest with a hidden cave where you need a key would be possible, just not to connect the towns.

About the graphic, it doesn't match the tmw graphic style and guidelines. Have a look here: http://wiki.themanaworld.org/index.php/Guidelines

The distance between the towns is just too big to have a cave connection.

But the idea with trapped miners, bats and sounds you can only hear with cat ears sounds interesting.

As several towns are planned on Argaes and Kaizei the idea could be nice for a big quest or sequence of smaller ones. I think better in Argaes than Kaizei as the last has already a set of caves to connect areas. Couldn't the explosion be "the big Earthquake"?