Where I live the only thing relatively flat is tow paths and rail trails. It's both glaciated and unglaciated Appalachian Plateau. I live on top of a ridge that is 1,250 ft. Less than a mile away its 830 ft. It's an area of nasty little short steep hills all over the place. 6-20% grades. A constant max effort then nothing and back to max.
Last week I took one of those sand two tracks under a 256,000 volt powerline. I was on my 1,100 watt e fat bike and still had my ass handed to me. Sand with grades over 30%. I had Maxxis Minion 4.8" tires at 5 psi with 42 tooth Chainring and 46 tooth cassette ring pumping out 160NM of torque at about 3-4 mph. Up over the handlebars and still looped out a couple times. When you are going to hit deep sand you get rid of the bike at the first sign things are going south. The dog in the back pack on my back was not really very happy with me. They put power lines where nobody wants to do anything else. On a couple of the climbs I throttled the bike and let it drag me on foot up the hill. Like being drug behind a four wheeler. Max heartrate in 10 feet then rest holding both brake levers. The only way out once you go down one of those grades. I don't think I will try it again. About and hour and a half for 4 miles Old people don't belong doing that stuff.
It doesn't look as steep as it is. Notice there are no fresh vehicle track, only animal tracks.