Route 105 is a sea route which connects between Routes 104 & 105. Dotted around the route are various small islands where items can be found. It also houses the Island Cave which unlocks after opening the Sealed Chamber and contains Regice. To open the cave in Ruby/Sapphire, you need to stand in front of the braille for two minutes while in Emerald, you need to do a lap of the cave.

Marine Cave
In Emerald, there are rare occasions where strong rainfall will appear within the route and open up a new patch of water open to Dive which gives access to Marine Cave. They are located as seen here

Special Moves used in Route 105:
Surf