Iceland has been a major travel destination over the years, but for good reason. It's essentially a theme park for nature enthusiasts. There are countless stunning waterfalls to explore, glacier lagoons (and yes, you can do boat rides or glacier tours during certain times of the year), black sand beaches, and hidden hot springs.
Both Winter and Summer have their own pros. The Winter means there's a pretty high chance you'll see the incredible Aurora Borealis (aka the Northern Lights) and everything is covered in a pristine blanket of white snow. The Summers are very green, though still chilly, and you'll have a bit more flexibility in terms of driving and seeing more throughout the day since the sun stays out up to 21 hours.