Short, relatively easy uphill hike with rewarding views of Mount Ruapehu and Mount Ngauruhoe (Mount Doom).
The trail for this hike starts next to the bathrooms that are about 150m down the road (south) from the Whakapapa Visitor Center. If you're standing in the road looking at the bathrooms, the trail head is to the right.
You will be going uphill the entire time without much flat trail, but it's not for too long. The trail starts out going through the woods and then after 10 minutes or so you'll come out of the woods into the brush, where you'll start to climb makeshift stairs. After another 20 minutes or so you'll get to the top of the stairs, where there's a big wooden table-looking object. We sat here for 20 minutes admiring the views. You'll have a nice view from here of Mount Ngauruhoe, Mount Ruapehu, and the Chateau Tongariro Hotel.
Just go back the way you came to get back to the trailhead.