In previous and subsequent episodes a door that is used as an entrance and exit to the Five-0 office is used as a janitor's closet in this episode only.
The crooks outfit what is supposedly a vacant building to look like the Five-O offices. When the bookshelf is being delivered to "Stash", however, on the left side of the door there are dirt marks on the wall where a framed picture had been hung, revealing that this was in fact the regular Five-O headquarters that had been temporarily divested of its furnishings.
The car being dredged out of the water supposedly in Hawaii is stock footage, the ship at dockside is from San Diego.
Although Walker says as a building contractor he can remember details, how can he recall exactly where he was taken on his earlier journey, and especially where to make turns? In that scene, he was told to stay low and out of sight after the vehicle was "fired" at by the co-conspirators, so he was unable to eyeball the route.