The national park of Mount Kaz (known as Mount Ida centuries ago) between northwestern Çanakkale and Balıkesir provinces is one of the most oxygen-rich regions not just in Turkey but around the world. Overlooking the Gulf of Edremit, it hosts a large forest and many natural wonders, ranging from waterfalls to canyons and creeks.
Ballıkayalar Nature Park just outside of Istanbul in northwestern Kocaeli province is a preferred location for trekking thanks to its many trails, some of which run along a scenic gorge. The park has many picnic areas and camping locations. It is the ideal destination for light trekking.
The Kaçkar Trail, which runs through the Kaçkar Mountains of northeastern Turkey, is one of the most unique and eye-pleasing trails in the country. The trail can take around 30 days to complete if one wishes to explore all the natural beauty that the mountains offer. Several glacial lakes and valleys as well as plateaus are located in the area.
You can read more about trekking routes in Turkey here.