I really enjoyed Kickapoo but it's within the 100 mile border zone. We got stopped by plain clothes chuds with their fingers on the trigger of AR-15s. It was remote enough they could have killed us and rolled is into a ditch. I'm not going back until Trump is out of office.
Kickapoo Cavern State Park and Devil’s Sinkhole State Natural Area take some planning (and driving), but they’re both worth the effort. https://www.texasmonthly.com/travel/least-visited-texas-state-parks/