One of my favourite hiking area in Slovakia is Mala Fatra (Low Tatras) national park. I have been there many time as this limestone area is great not just for hiking but also for Alpine flowers and European orchids. Many unique species of birds including Wallcreper and Falcon. You can follow ridge walkks, discover nice Janosikovy Gorges and meet local freindly people. I always like to go back. Great time in autumn.