Can you go back to Bunker Hill after the mission is complete?

Can you go back to Bunker Hill and other locations once the missions are complete? Also, is it possible to free-roam while sailing a ship or do you have to do a naval mission every time you get on the ship? One last question, for the screenshot Gamespot used for the review for this game (the one where Connor is standing on a rooftop with tomahawk in hand overlooking a snowy city with a ship in the pier), where is that in-game? I want to go there.

When I say "go back to Bunker Hill", I mean to free roam... not to re-do the mission.

bump

anyone?