In my opinion running outside is great-and uphill running -even if you do it very slow will build up your stamina quickly.
Apart from that skipping! 10min of skipping is as effective as 30 of jogging. Trust me after 10 min of skipping you will feel your legs the next day. Skipping is also great fun-try skipping from side to site, hop ob one leg a few times, kick out your legs (with some good music it can be really fun)
You can also try a cario workout which really trains your whole body (I do that at gym at work)
but you can also do that anywhere. Take 20 min to do that -dont take any breaks between excercises and you feel you have done 1h
Start with 3 min of running without a break do 1 min of press ups, 1 min of squats, 1 min of lunges
3 min of running again followed by 1min of upper arm work - again do 3 sets of 1 min
3 min of running followed by 3 sets of 1 min excercises again
Afterwards do stomach excercises (rty to start with 3 sets of 20 sit ups)
As a goal try if you can do 10 min of skipping, followed by 80 press ups