Twentyone Mile Creek begins its long and steep journey from Rainbow Lake, high up and between Mount Sproatt and Rainbow Mountain.  Cutting between the two mountains, Twentyone Mile Creek flattens out somewhat, passes under Alta Lake Road, then winds its way through a deep and dark forest before flowing into the River of Golden Dreams near the end of Lorimer Road.  This hidden forest extends from Rainbow Park to Emerald Forest and between Alta Lake Road and the River of Golden Dreams.

Rainbow Park is one of Whistler's most popular sightseeing, picnicking, dog walking, relaxing and swimming beaches and for good reason.  The beach is south facing so every morning the sun rises from behind Wedge Mountain and the whole park seems to glow.  From the dazzling reflecting from the snow off of Wedge Mountain, Blackcomb Mountain and Whistler Mountain, to the amazing blue glow from Alta Lake.

Rainbow Park is one of the hugely popular swimming beaches in Whistler in the summer.  In the winter it is a spectacular vantage point across Alta Lake to Whistler Mountain and Blackcomb Mountain.  The beautiful ski run lines snake down the mountains and by December Alta Lake is usually completely frozen.  Hockey games occur at various spots on the lake and the Valley Trail leading to and from Rainbow Park is buried in snow and unplowed all winter.  When the heavy snow of December comes, the valley trail becomes a snowshoeing and cross country ski trail.