I recently saw a video about content in Syndicate that said there were coop missions in famous British landmarks.
And now I understand why on the board of the train hideout there was this on the left corner
You can see pictures of Stonehenge and Lindisfarne. Most of the places said had a dot on the map except for Winsor Castle, Dover, and Cambridge. Many dots of Ireland aren't linked with coop missions. The first time I saw the map, I believed it was an easter egg, places that Evie wanted to visit to discover Pieces of Eden or hints about Valhalla. Now, I think it was meant to be a menu to launch coop missions.
I could expand more on the British Brotherhood, they already cut Reuge's journal on the Aegis discovery.