The High Note Trail is Whistler Mountain's premier hiking trail. Thanks to a gondola/chairlift access combination, It starts right at the summit, with incredible views right away.
The 9.6km loop route has 430m elevation gain and 825m loss. For experienced hikers, it is moderate difficulty. There are some narrow sections and a very short non-technical rock scramble, but the rest is approachable hiking trail with regular ascents and descents (occasionally steep).
My friend Taryn from Happiest Outdoors has a comprehensive trail guide so I'd recommend checking it out first before deciding whether this is the hike for you. Keep in mind that the gondola/chairlift ticket is almost $100.
I would recommend getting on the gondola as soon as it opens. Buy your tickets online to avoid most of the (long) line. The chairlift opens a little later than the gondola but it's better to be early rather than late.