Trail starts at the east end of the Johnston Ridge Visitors Center parking lot. Need a USFS permit to park there. Trail is good most of the way and there is information on the hike here. You can actually see the peak from the trailhead and the majority of the trail is out in the open so make sure you bring sunscreen. Bring plenty of water as there is none along the trail. The hardest part is the last 3/4 mile which is steep climbing with switchbacks. Ran into lots of people along the trail but only 3-4 back towards the peak.
The top of the peak is completely clear and you can see Mt Rainier, Mt Adams and Mt St Helens. There is nothing to attach an antenna pole to except the radio shack and related structures at the top. Was not sure how that would impact my radio signal so I made do with a short mast tied to my backpack. I'm going to figure out a good way to get the mast up without a tree to attach it to.
Was fortunate to make my first contact with Randy K9VD in Everett on 2 meters who spotted me on 20 meters. One of the other chasers on 20 meters spotted me when I switched to 40 meters. Gotta love those chasers! Couldn't do it without them. Made 15 QSOs altogether.
The only problem I had was starting too late in the day. That resulted in hiking out the last 1.5 mile in the dark but my trusty headlamp helped out with that. Ran into a photographer who also started too late and we hiked out together. Not my favorite hike but the views from the top were fabulous.
See also: https://www.oregonhikers.org/field_guide/Coldwater_Peak_Hike
See also: http://www.willhiteweb.com/washington/fire_lookouts/coldwater_peak_lookout/st_helens_254.htm
Former lookout: https://washingtonlookouts.weebly.com/coldwater-peak.html