If you don't have any hills then try to find steps to run or walk up. If you only can find several stories just repeat until tired. Find a gym that has one of these.

There are several people that come from Florida to PA every year to do one of our hilly trail marathons. I believe they do a lot of walking lunges to prepare for walking up the hills.

I generally train for hiking /walking hills the same as I do for running (but that may not be the way you train) - duration and intensity (breathing, HR, whatever), but may put more emphasis on amount of climb than duration, depending upon my goals. I believe in specificity in training. If the race's hills are ramplike, then I train on ramplike hills. If they're steplike - rocks and roots arranged so foot plant is flat rather than dorsiflexed - I train on similar hills, if I can. I'll try to match types of hills in races (length, steepness, footing) with what I have available, if I can. Some hikes are "easy" (in terms of HR/breathing), others are more toward LT (think climbing 1500ft in 1.2 mi at 1-hr race effort or close to it).

If you don't have real hills, you can use bleachers, bridges, parking garages (when not busy), etc TM are good to simulate ramp-like hills while the stepmill (escalator) is good for step-like hills. If you're actually training for hills, don't forget the downhills. There's some strength stuff that can help your legs if you don't have something available.

[Note: we have a popular climbathon where you run/hike/crawl up a trail on a hill (2000ft in 2.4mi) at a ski area, take tram down, repeat, for 10 hr. Results are reported in terms of how much uphill you achieve with only full laps counting. So sometimes total vertical is the parameter being aimed for. This is why I suggested that the way I train for races or runs/hikes in the mountains may be different than the way you train.]