For those who have never been to the Pacific Northwest, visiting Seattle is a must. Tourist friendly areas such as Pike Place Market and the waterfront are a great place to explore.
For those staying on the island, the wedding venue is just minutes away from downtown Langley. A small and walking friendly island town full of good restaurants, beaches, boutiques and breweries.
Mt Rainier National Park is a couple hours south of Seattle and makes for an excellent day trip for those extending their stay. Note that you may need to reserve your park visit in advance.
For those extending their stay and looking for an adventure, Olympic National Park and the Pacific Coast can easily fill days worth of your time.