So, the tough ones I've done, in rank order:

1. Mountains of Misery. 103 miles in the Blue Ridge near Va. Tech and a final climb that comes with 98 miles in your legs, and that damn climb has 15-20% grades. 10,000+ feet of climbing.

2. Triple Bypass. A close second to MoM, practically a tie, but for different reasons. At 120 miles, a "super century". Climbs much lower grade, thank God, but LONG and a real challenge for flatlanders; there's 30% less air at the top of Loveland pass than I'm used to! 10,000+ feet of climbing.

3. Crater Lake Century. One tough sustained climb to get to the rim of the lake, and then a surprising amount of climbing around the periphery of the lake. Screaming descent on the way out. Per mile, probably the most beautiful ride in North America. 7500 feet of climbing.

4. Civil War Century. Beautiful ride ride around Catoctin Mountain area in Md. 7,000 feet of climbing, nothing to radical except for one nasty but short climb at ~60 mile mark. Somehow the rollers in the last 20-30 miles really kick my butt.

5. Seagull Century. This one is easy and I have a fondness for it because it was the first century ride I did. Flat as a tabletop, but often windy and it seems to pour rain about every other year.