Overview
This guide will be a very basic, line drawn tunnel guide, that will help players starting out on the Marine tree or who want to eat something other than Megalos crossing the land bridges. This guide is a work in progress, so a complete understanding will have to be explored and learned by you! If there are any trenches that I have missed, please tell me in the comments of this guide. So far, I am only focusing on the 3 trenches in/near the Bermuda Lagoon. Warning, this guide DOES NOT inform you of any paths that are not accesable during high or low tide, as I have a life and can not spend too much time studying the tunnels.
Ancestral Plains Map
~ Stoid
The Swamp Trench
The Swamp Trench is located between the swamp on Mountain Island and “The Step” Island. As shown here:
Inside the trench, there are 4 tunnel doors, yet one is blocked, creating a “T” shaped formation as shown here:
The tunnel pointing to the left in this photo leads to the Landbridge Trench as I like to call it.
The tunnel pointing upward in the photo leads to these lakes/caves following these directions:
1. Follow the path.
2. Make a left. To the right there is another entrance to the mainland level.
3. Go through the cavern, where there will be a tunnel on the left side of the wall.
4. Follow path until you reach the roundabout. Right leads to the “Bridge Cave” where there are big carnivore families (As shown below). Left leads to a dead end, and forward continues the path.
5. If you followed the path by going forward, then you’d come upon a cave opening near “Lower Bridge Lake”
The tunnel pointing downward in the photo leads to these lakes/caves following these directions:
1. Follow the path.
2. Make a left, as going right leads to a dead end!
3. making a left at the conjuction allows you to find a fresh water source inside of “The Step” Island! (As shown here) making a right continues the path.
4. A left shortly after leads to the entrance to the cave inside “The Step”. Making a right continues the path.
5. At the roundabout (Sounds like a gps lol) a right leads to a dead end, a left leads to a continues path, and going straight also leads to a continued path. If you made a left, then now you are entering “The Step” Trench area, which is a different section. Continue reading from step 2 of “The tunnel pointing to the left in the photo leads to these lakes/caves following these directions:” If you went straight then you are now entering “The Ambush” Section of this article. Continue reading from step 7 of “The tunnel pointing to the left in the photo leads to these lakes/caves following these directions:”
“The Ambush” Trench
I call this trench the ambush trench, as there are many aquatic plants a hilly surfaces within the area to allow for Mosasauruses and Kronosauruses to hunt and ambush from. There are two tunnels with one being higher than the other in altitude, as shown below.
The tunnel pointing to the left in the photo leads to these lakes/caves following these directions:
1. Going straight is a dead end, so turning left is the only option.
2. When you make it to the conjunction, turning left is a dead end, so right is the only option.
3. When you reach the conjunction, a left turn is a dead end, so going right is the only option.
4. Right after, turnng right is a dead end, so going straight is the only option.
5. When you reach the intersection, to the left is a dead end and forward continues the path where you will be lead to a conjunction that if you make a right(Straight leads to a dead end), will lead to “Lower Bridge Lake”! (As shown below) 
6. A pointless intersection, as you will see has two blocked tunnels and the only option is straightforward.
7. By continuing, you will reach an intersection where going left is a dead end. Going right leads to tunnels connected to “The Step Trench”, and going straight leads to various cave opening to “The Step” Island. This is where you must continue and reverse the directions starting from step 5 on “The tunnel pointing downward in the photo leads to these lakes/caves following these directions:”
“The Step” Trench
As shown in the map at the beginning of this guide, “The Step” Trench is nearly right in front of “The Step” Island or right off the coast of the Lowland Ponds. There are only 2 tunnels, which makes it easier, for me and you to differentiate from because one has more rock on the outside than the other.