You need to follow the trail up to Mueller Hut so please read my description on that. Alright so once you’ve made it to Mueller Hut (which is already a solid mission on its own), you’ve got the option to keep going up to Mount Ollivier Summit. It’s only an extra 700 metres from the hut, but don’t let that short distance fool you, it adds a decent bit of effort. All up, you’ll do about 11.1 km return and climb around 1,150 metres of elevation, so that’s an extra 700 metres distance and about 150 metres more elevation on top of the Mueller Hut track alone.
I really wish I did this part, but I was way too cold and there was a heap of snow around when I went. It’s not just a wander either, this section heads into advanced avalanche terrain, so only tackle it if the conditions are right and you’re properly prepared. But if you do make it up there, you’ll be rewarded with insane panoramic views over Aoraki/Mount Cook, Mount Sefton, and all the glacier-filled valleys below.