Hiya Talos! When they send you to see Shiniwiki, you should climb down a ladder (or fall down like the rest of us do) and be in some tunnels. From there you will find two ladders up, one of them takes you up to a hut where he is. The ladders are both in the tunnels, but are kinda far apart. If you are swimming around, you must be outside the tunnels. You walk in the tunnels, not swim. Also, you can look at a map on Rick's site here:
http://www.volberding.com/WHints/index.html
Hope this helps you out!

Mammawlin