I find the HHH course to be pretty flat. What hills there are, are relatively short and not steep. You really should try it, I think you will find it is easier than you think. If you aren't up to 100 miles, they do have a 100K (62.5 miles) that is a really nice ride. Rest stops and aid stations are located every 10 miles around the course so you are never more than 5 miles from medical attention if you need it.
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