I spent $15 taking a ferry from downtown Portland to an island off the coast of Maine. It was a great day trip.

Located in Casco Bay, Peaks Island can only be accessed by ferry boat.

Less than a thousand people live on Peaks Island year-round, though that number increases in the summer. A lot of the island's residents regularly use the ferry to commute to and from downtown Portland to go to work, attend school, or run errands.

So, the ferry typically runs pretty frequently between the two places. I appreciated that this gave me more flexibility around leaving and coming back from my day trip.

My round-trip ferry ticket cost me just $15. The ship left from Portland's waterfront area just off Commercial Street.

I chose to sit on its top level to maximize my views on the short ride, which only lasted 17 minutes.

From the water, I spotted Fort Gorges, a former military fort; Bug Light, a lighthouse in South Portland; and Mackworth Island, a state park.

Once I arrived, I loved that our ferry dock was just a few minutes' walk away from an ice-cream parlor, seafood restaurants, and shops renting golf carts or bicycles.

The island seemed too big to explore on foot, so I knew I wanted to rent some mode of transportation. It would've cost me $100 to rent a golf cart for two hours or $20 for a bike, so I chose the more affordable option.

When I got my bicycle, I was given a handy map highlighting the island's various landmarks.

I loved riding past the brightly painted houses and rocky, pristine-looking beaches. They seemed nice and quiet, a contrast from popular beaches in Portland that can get pretty crowded on weekends.

At one point, I took my bike over to Battery Steele, a concrete military fortification from the 1940s that's covered in colorful graffiti.

I was able to follow a trail up to the structure so I could look around its tunnels and rooms. It was bigger than I expected and felt easy to get lost in, but the views from the top were great.

I also enjoyed stopping by the island's Umbrella Cover Museum, which features thousands of umbrella covers that have been collected over the years.

The island also had several art galleries showcasing paintings of Portland and other towns in Maine.

My day trip was pleasant and affordable, especially since ferry tickets were cheap and the ride was so short.

Peaks Island felt like a nice escape from the hustle and bustle of downtown Portland — plus, riding a bike around all day was a great workout.

I'd go back, though I might try taking the ferry to a different Casco Bay Island for my next day trip.