I've been up a few steep hills in my life. Here's a few.
Ashford, WA to Paradise on Mt. Rainier. 1,844ft to 5,417ft over 22 miles. The first 10 miles aren't that big of a deal. It's just gets progressively steeper as you go.
Mt. Lemmon in Arizona. Start at about 2450ft and top out about 8,200ft over 29 miles.
Koh Phang-an, Thailand. The paved road out of Had Rin to the western part of the island. Road this beast back in 1999. A huge steep hill but maybe only 400m long. Steep as can be. Can't get up it when it rains as the rear tire on the mtn bike just slides out. When it is dry you have to adjust your weight to keep the front tire from coming off the ground.
Doi Suthep in Chiang Mai, Thailand. Climbed it on my road bike.
Doi Suthep climb via Chiang Mai | 18.3 km | 1575 m | 6.7% - Climbbybike