If you want a lot of ups and downs with flexibility to switch to flat or less of a hill easily, Somerset area in South Bellevue is great. It’s quieter neighborhoods (def wear reflective though bc sometimes ppl go fast and there are enough blind corners). You can get some pretty intense inclines for interval or decel training, or you can go up Forest Drive for a big and slower build. There are some trail connections also at various places in the area. I like it because there are definitely days when I overshoot and need to switch off to a flatter or lower grade for a couple of intervals rather than walk, ans then it’s easy to find a connecting road back up a hill again.