How do I infiltrate the building on zone E3 in Expedition?

[HailedProminent]

I already know the professor is there after checking the wiki so as not to waste my time checking all three locations but I can't even seem to find an entrance to that section of the map! I wandered as far east as L6 in the fetid marsh (I think, this grid system is really confusing to my feeble mind and I had it backwards for a while which was fun...) trying to find a entrance but I keep getting turned around. Parked my jet ski on I4 where I am now. I saw one post talking about some caves in the south east corner of the map you can use but no more information than that. Do I just need to keep going around?

[Amannamedsquid]

There are 3 ways to get the professor out. The first is to try to negotiate with Captain Grim, need to talk to Razor and you'll be taken directly to the Captain. The second way is to fight your way to the professor. The main entrance of the pirate base is at G1, which can be reached if you go south of G3 or H3. If you're looking for a more stealthy approach, there is a hidden cave on the island at E4 that leads to a secret entrance to E3 but you need 11 perception to notice it.