I know Florida and Illinois are technically the flattest states, but I am sure it would be a challenge to find a good spot on the Kansas side of Missouri too!  River valley areas are probably the best bet aside from indoor gyms.  I concur with Marc that you should take qualified instructor led courses as a starter, then see if local areas have excursions you can participate in.  Friends of mine who still qualified to guide during the day offer rappelling for groups or individuals at reasonable prices.  This way you know the setup is good as opposed to a group blog post somewhere less reputable which could get you into hazardous situations.

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