Land-breaker started from the time he went looking for his Highswords. They were not in the Old Empire's lands—which was pretty obvious. Otherwise, the Emperor and other third-rankers fighting the demons for years in the alliance army might have sensed them.
The Land-breaker began searching along the sea route many ships had taken when he was at the edge of the Old Empire. After following a ship for a few days, he found an island hundreds of kilometers away from the mainland. It was mostly just a rocky island with patches of sand here and there, but behind it was a cave entrance where ships could enter.