Cross watchtower (The Elder Scrolls 5: Skyrim)

Question on the quest to Investigate a place called Cross watchtower. The purpose of the search - Steel greatsword of souls.
I do not remember who gave the assignment, but the essence is this: I never found such a place by that name, because on the map it was not marked. Random BlueGene on the watch tower of Falkreath was still found the sword, but the direction indicator in the task has not changed. Then I noticed that the indicator of this task leads to a House of the warrior in Whiterun, and somehow, in this very house the indicator goes under the floor. In the house Adrianna Avenice and Ulfbert Razyarenny Bear anything about this task does not explain. What to do?