Great place for day out
There are 2 tracking route in general in jangtaesan area. If you come from daejeon, when you alight from the bus, go right for longer track and less people and this one is not advertised that much. However, if you want to see the place that is advertised or reviewed by many traveller, go across the street and you will see the main entrance (the picture). This place offers 3 route of trekking: (1) 1.3 km, (2) 3.34 km, and (3) 10.35 km.
I pick the second route 3.34 km and I found that the filed was not that hard but you need to be careful with your step. And applying bug repellant before trekking would help you a lot.