Thunder Lake is located about 20 kms west of Barrhead, in the beautiful and well-maintained Thunder Lake Provincial Park. From the parking coordinates, about 500 m along the lakeside trail you'll come upon four benches overlooking a quaint little sand beach: a great place to do some leisurely wading along the shoreline (weather permitting of course).
The cache is a little less than a 10 m bushwhack off of either of the two main trails that intersect nearby.