Black Rock province's Riverdale Town.
It didn't take long for Sato to return to 'base'. It took him at least an hour since his departure from the group before he could reach Riverdale. This was because with the Caventry's authority and with a [Teleportation Rune], he was able to jump directly to the 1st floor of the Outer region or even the entrance. Sato had chosen to go to the 1st floor before wearing a black cloak to hide his identity and departing the area.
Originally, with one of the highest authorities in the Caventry, Sato was granted a [Void Opening key] that could not only send him to the Great Hall but could also open wormholes to close locations. However, he needed to 'store' the destination within the [Void Opening key] else he wouldn't be able to locate a stop. It was because of this that Sato had taken 'too long' to reach the town. If it were with the [Void Opening key], he would have done so almost instantly.