I have selected Jupiter Creek Diggings. This was a gold mining area from around 1869 to 1930. It is now part of the Kuitpo forest reserve. You get there from Echunga. Follow the large signs on the Echunga to Mylor Road. Leave your car in the car park and take the hiking trail. It’s a 3 km walking track that takes you to all the mine shafts in the area. There is one you can go into that runs 60 meters underground. You come out by climbing a vertical steel ladder. You should take a torch and I recommend a hard hat. The trail leads through stringy bark forest and there are birds, lizards, butterflies and lots of trees. We went back there today to scout around. Unfortunately there are no toilets and you need to take water and food if you want to drink and eat.
My other recommendations are Anstey Hill which is North East of Adelaide and has a walking track, ruins, wildlife and flora.