Is it possible to train for mountains/hills in a place that has neither i.e. Miami? I'll be in Miami all summer and I want to get good at climbing, but I don't think it's possible.

Ride around in your biggest gear all the time?

For climbing you want to increase your sustainable power/weight. For sustainable power, do long intervals (20+ minutes) at where you are breathing real hard, but not yet gasping for breath. If you have a power meter or HRM, do a search for 'sweet spot training' or SST. Descending will be a problem. - TF

Is it possible to train for mountains/hills in a place that has neither i.e. Miami? I'll be in Miami all summer and I want to get good at climbing, but I don't think it's possible.

Even flat areas will have some hills-- look for overpasses. If traffic isn't too much a a problem you can do some repeats on them.

Headwinds are like invisible hills. Go out on a windy day and head straight into it.

Az

buy a trainer and everything else everyone said here

Any multi-level parking garages around?

Don't have the money for a trainer, but I guess I can do the rest. Does riding up and down a bridge a lot really help? It seems to me that the fact that you're only ascending for a minute or two wouldn't help all that much.

Find a spin class!

I have a problem similar to the OP's. I probably have more hills here in Michigan but its still flat relative to other places in the country. No matter how hard I try and mix it up, I cannot get more than 30 feet per mile of ascent on my routes.

I wondered if doing intervals while standing, say about two minutes each with an equal period of rest, would have any benefit for climbing ability?