Two come to mind. The first, and less difficult of the two, is Great Meadow, where the Virginia state meet is held. The course starts on a very flat, roughly 600 meter straightaway. Then, the course dips down and to the left. The course then takes runners up a short, but steep hill. Then, runners enter into a small loop in the woods that has rolling hills. Upon exiting the woods, the runners reach the one mile mark. This is where the course gets tough. It dips down and to the left, then goes up another short and steel hill. After, the runners get a break and have a long straightaway on uneven grass that can hurt your foot if you're not careful. The runners then get to a hairpin right turn where the ground is often muddy (it's usually cold, rainy, and windy here, as it's in the Shenandoah Valley). Then the runners go left and down, then take another sharp left turn that goes straight into a shin-deep creek crossing. Afterwards, runners go up and to the left on a steep hill. Another hairpin left turn is experienced, where runners quickly go down and to the right, then immediately back up. The runners then run downhill in a Z shape. The second mile marker is in this area. Then, the runners run a long stretch before turning left and going up yet another steep hill, the final one on the course. The runners run to the left and then back down the hill, then take a sharp right into the finishing stretch. The finish is demoralizing - it is close to 800 meters long and the finish line only seems to get farther away. Runners often say that it's among the toughest courses. Times rarely go below 16 here.
The second one is Kernstown Battlefield in Winchester, Virginia. This course sees the Judges Classic invitational held by John Handley high school every year. The start of the race is one massive hill. It's about 200 meters or more of a steep uphill. Runners then take a sharp left and immediately go up another short but very steep hill. Runners then turn right and enter the woods, where there are many large downhills followed by long, strenuous uphills. Runners then turn left and go up a long, steep hill that brings them back to the top of the second hill on the course. Runners then get a long downhill where they pass through the finish line and go down. The first mile is about 100m past the finish line. The second mile is fairly flat, yet times seem to always be slowest here. Runners cross through the parking lot and go up and to the left around some houses. Then, runners pass the infamous "stinging corner", aptly named as there are tons of wasp and hornet nests here that keep coming back regardless of how many times the battlefield gets rid of them. Usually around 25-35 percent of the people who run in each race get stung. Runners then go on a very short downhill and take a sharp right back into the starting hill. Yep, you have to do it twice. After traversing the starting hill, runners have to go up the second, steep hill AGAIN. This is where most people admit to walking on the course. Then, the runners turn into the woods section again and encounter the second mile marker. Then, runners go through the woods again but instead of going left as they did in the first mile, they go right, where they go on a long uphill that eventually turns left and goes into steep rolling hills. Then, runners go on a flst road for roughly 200m and then go up a steep hill. Then, runners encounter a downhill followed by another steep uphill that brings them back to the long downhill right before the finish line. This is where runners get simultaneously the most relief and the most grief, as the finish line never seems to get any closer. Times don't go below 16 here.
I know these two courses aren't as tough as a lot of the others (Bear Mountain in NY, for example), but they're definitely the two toughest ones that I've run myself.