Hello~ I need your advice.

Hello. I'm Sean from South Korea. I was a student in Auckland and I'd finished my school. So I'm travelling now before getting back to Korea on 12th, August. Travelling itself in New Zealand is fantastic. I particularly love the nature of this country. So to enjoy more this country when it comes to the nature I'd like to try a bit of trekking or short-term walking. I originally wanted to do the Northern Circuit in Tongariro National park but having considered my experience and the recent weather I gave up doing it. So I need your help, from everyone. Would you recommend me some of walking tracks or trekking courses in North island? I might be doing Lake Waikeremoana walk as an alternative. I'm reasonably fit and taking 3 to 4days courses would be perfect to me. Actually, I really want to see more exotic scenery like volcanic remains not just some bushes. And it would be very good if I get the place you recommend by public transport easily. I'm looking from hearing from you guys. Give some advice to get me unforgettable memories before leaving this beautiful country. Thanks guys~