We have our stronghold now, our home away from home, our bastion if you will. In keeping with the approach from Bastion we get little side tasks in the form of time trials and undoubtedly other trials that will test my ability with different elements of the game.
It is kind of neat to have it, but I am not sure it fits thematically. Red just doesn't seem like the kind of hero to sit back and relax while she has a job to do and the city seems to be being converted without her. It made a lot more sense in Bastion because story wise it was structured as the hub you strike out from and return to. Here the sandbox is just the kind of place you seem to run across entrances to periodically as a chance to take a break.