I have a three story home... My third floor shower ( whch has not been used in 2++ years)

Has a nasty smell... Need help... Where do I start...

For your shower, First remove the strainer,(TIP: put the screws in the soap dish. They will be hard to replace if they go down the drain.) Now work your snake past the trap and 6 or 7 feet beyond. When you pull the snake back it should have the hair that was clogging your shower on the auger tip. Now pour 1/4 gallon of bleach down in the trap and let it set over night. Next morning pour a pan of boiling down the shower to clear what's left and make your drain smell nice. Good, luck, Tom