Out of the ordinary

Hi folks, I'm from Malaysia. Im planning an epic (by my standards) trip to NZ sometime next year and stumbled upon this wonderful forum. I'd prefer not to put on a large sun hat, floral shirts, and camera at the ready doing cheeky touristy stuff. Im wondering which peaks in NZ are categorized under the 'challenging' bunch. To be more specific, the hardest or the best. I realise it should be rather subjective but I'd like to hear your thoughts as well. At least, it gives me some clue as where to start with. Thank you in advance. Julian