impossible underground

Exploration Stage: Burned-out Estate
From: Harper McGill
Description: Yes, it is. Eli, your floor plan was probably created after you bought the house. I have the original blueprints. I took them with me when I was evicted from here. I went through the yard with it before you came and disturbed me, but I dropped it because of your mess and your saying. Please help me find it!
Completed: Thanks for helping me find the first floor plan. You can see for yourself that there was always a basement here. But the walls were built before I was born. I don't know why, I've never been in the basement, but it's obvious I need to go there.