To get this achievement, you need to complete the Dolphin escape on HMP Offshore.
For this escape you'll need intelligence stat of 70+
A bit of strength and a weapon will help as well.
You will need a readied fishing rod and a red plastic key, so you gonna need to search for a few items:
- piece of string
- a juicy worm
- a comb or a toothbrush
- a lighter
- talcum powder
All of these can be found in desks. I had a few problems finding timber. I got one from doing the furniture work, however I later found a piece in a table and on a knocked out guy, so you have multiple options.
Once you have these items create:
fishing rod = timber + piece of string + paperclip
readied fishing rod = fishing rod + juicy worm
molten plastic = comb/toothbrush + lighter
putty = talcum + toothpaste
put the putty on you and go beat up guards until you find the one that has the red key. Take the red key, combine it with the putty. Put the key back on the guard and combine the red key mould with the molten plastic. You should now have a red plastic key.
Now put the readied fishing rod and the plastic red key in your inventory and go all the way to the left to where you can go down and then through a red door. Go all the way down in this part.
Now exit through the red door south and walk along until you see the Dolphin Snooty.
Next to the dolphin is a hole in the rail. If you have the readied fishing rod, you can fish here.
Do that and you'll catch a fish. Give that to Snooty.
Now you'll have a quest marker, to find a book. I would advise you to first go back to the main platform and then go all the way to the right, as if you take the walkway below, there will be a metal detector at the end and multiple cameras.
Once you find the book, you'll get quest markers to find 3 items in inmates cells.
Milk, Flour and Sugar. Combine these to make a cake and bring that cake to Snooty.
You'll escape on Snootys back.