Thicket Excavations is one of the largest locations in Sanctuary Sector. You will have to visit it at least twice to fully explore it because part of the place is flooded by water. You will pump the water out during the Pull the Plug quest. However, the water will not be pumped out immediately, it will take at least few days. It is wise to wait, as you will gain many valuable items here.
Two mirelurks will attack you after you activate the pump.
In the trailer on the left you will find the Taboo Tattoos Magazine which will unlock an additional face tattoo.
Once you return to the location few days after activating the pump, it will be occupied by a group of raiders. Keep it in mind and try to eliminate them one after another. At the bottom of the excavations you will face their leader.
Few mirelurks can be found at the bottom of the excavations. You have almost no chance in direct combat, so it is better to kill them from above with the sniper rifle or grenades.
You can use the elevator on your way back.