I have used two different ways indoors to prepare for hill climbing. When on an indoor trainer, I do intervals. I am not a gear masher and don't recommend high gears to simulate hill riding. Stay in easy low gears and pedal at a high rpm after a good warm up for 1-2 minutes if you can. Then back off on the rpm's and recover for 1 -2 minutes and repeat - it will build strength. I normally ride for 30 minutes. I do a 5 - 10 minute warm up, 10 minutes of intervals ( I ride hard for 2 minutes and rest for 30 seconds and repeat - but I have been riding for 30 years) and then 5 - 10 minutes of cool down. that's my first recommendation. the second is similar to what was already suggested - step ups. Find a two step, step stool and take hand weights and climb up and down the stool. This will build strength in your legs too. Good luck. Bekki