I don't know why, but I was really excited to go to the tannery in Fes. It's reputedly quite stinky. Everything I'd read talked about how bad the stench is. First they soften the fresh hides by putting them in vats filled with pigeon poo and water. Then they dye them various color to make shoes, hand bags, valices, jackets, etc.
There are many balconies overlooking the large tannery. No matter which one you go to, they hand you a bunch of fresh mint to use to cover the stink. Luckily, the day we went the smell wasn't too bad, though I did use my nosegay of fresh mint a few times.