Whether you enjoy paddle boarding / kayaking or just enjoying the mountain views Lake Granby is a beautiful place to visit.
Andrew and Tara have backpacked near Granby, CO in the Never Summer Wilderness — a great option if you're looking for less crowded hiking. Otherwise, this link highlights some awesome hikes closer to Granby Ranch.
Rocky Mountain National Park is full of great hikes, and a scenic drive. This entrance is only 25 minutes from Granby.