"Down the hill" is a familiar way to say the city is located below another one on a mountain or hill. There is not a good synonym that captures all its senses. You could say "below," but that doesn't have the idea that they are both on the same hill.

The expression "It's all up hill from here!" and "It's all down hill from here!" mean that things will only get better or things will only get worst.

The expression "It's all up hill from here!" and "It's all down hill from here!" mean that things will only get better or things will only get worst.

I've never heard that expression before. I'm gathering you have City A, which is located ON some hill somewhere. And someone is trying to give you a description of it in relation to City B. They might say, "Markstown--that place is just down the hill from Jamestown" (these are fictitious cities I made up). Though I've never personally heard someone use a hill as a point of reference, it is possible.