Credit: James Baigrie

Problem: Subterranean Smells
Guests wouldn't know that your beautifully appointed basement used to be a dank concrete bunker―until they take a whiff.
Solution: Cut an onion in half, place it on a plate, and leave it in the basement overnight. Once the initial salad-bar aroma dissipates, you'll have fresh (non-oniony) air. Like magic!