A tarn is a small lake not a town and a snicket is not the same as an alleyway... Usually a snicket is a small narrow pathway that can be quite hidden away and is often only used by locals. That is probably not the best way it can be explained but alleyway is certainly not the right term. Path would be more appropriate if you are looking for a one word answer but honestly the only word that can properly describe a snicket is "snicket"