This cache is on the Pacific Crest Trail. The Iron Horse trail can be seen from a viewpoint next to the cache, but sadly these trails do not connect. The tunnel can be found a few hundred feet below this cache.
This cache is about 3 miles from the PCT Snoqualmie Pass South Trailhead and 2 miles from the Windy Pass Trailhead. The shortest route would be to come from Grand Junction (GC3T3YX), but the road gets rough after that point. You are looking for a small lock n lock close to the trail, no need to descend or ascend at all. There is an unactivated Party At Farrel's Place geocoin for FTF.