Kath and I had a foggy trip up to this aptly named peak. Start at top of Porters Pass (70km or so west of Christchurch on way to Arthurs Pass, plenty of car parking). Basically start walking up the shingle / scree / alpine shrubbery on the north behind the display panel. A nice view if the mist wasn't rolling around us.
Takes about 2 hours for unfit people such as myself to get to the top and about an hour to get down. It's a very exposed ridge line all the way up to it and there was a rumour about a false peak before the real one, but we didn't spot it, possibly due to the bad weather.