There are magnificent waterfalls to view within an hour's drive from Volcano-
Rainbow Falls (as seen in the photo to the left) is located off of Wainuenue Avenue in Hilo, just follow the signs towards Hilo Hospital. When you get to the V, turn off to your right and look for the "rainbow" (there is almost always a rainbow overlooking the falls!). The falls are almost visible from the road. Parking is FREE! Across from the falls you can purchase beverages and food at the Farmer's Market.
On the way to Akaka Falls (as seen in the photo to the right) take the turn off onto the "4 Mile Scenic Drive and discover the beauty of Hawaiian Tropical Botanical Gardens you'll be amazed at what you'll see! The drive is a pleasant one, somewhat off the beaten path. Driving time from Volcano is about 35 minutes to Hawaiian Tropical Botanical Gardens and then about another 15 minutes to Akaka Falls. Akaka Falls offers a pavilion for picnics and public restrooms are also available.
Not a waterfall nor is it considered a botanical garden. However, Liliuokalani Gardens in Hilo is definitely worth a visit! Plan to spend about an hour to leisurely walk the perimeter of the Park. Adjacent to Coconut Island located on Banyan drive, it is about a 30 minute drive from Volcano. Follow Highway 11 until you get to Ken's Pancake House, at this intersection continue straight along the Bay front past the Golf Course (it will be on your left), Liliuokalani Gardens will be on your right. Its a great spot to view the harbor and enjoy a picnic!