GABF week is starting to get underway in Denver even before the main event later this week.

Tuesday, The Museum of Nature and Science hosted an event called "Beers made by Walking".

About 30 brewers from around the country brought beers inspired by ingredients that could be found in hikes and trails.

Some used fruits such as apples, peaches, and plums. Others added local herbs and some included ingredients rarely found in beer, like sumac, juniper berries, lavender, and even pine needles.

One even went to the great lengths of brewing their beer inside a hollowed out aspen tree for the event.

A few breweries from North Carolina and Illinois joined the locals for the event, which sold out this year.

Of course the main event - the Great American Beer Festival - starts on Thursday.