One of the most popular activities to do in Iceland is whale watching! There is an abundance of cetacean life in the waters around the country. Reykjavik Harbour, located near the city center, is a bustling hub for whale watching and puffin tours, as well as Northern Lights cruises. There are several companies with meeting points here at (or very near to) the harbour but my recommendation is Special Tours.
From May until mid-August you can add puffin watching to your tour. And, although more expensive, RIB tours are great for seeing more whales from a better vantage point. The ride on a RIB is also a bit more exciting.
Whale watching tours are available year-round however, sightings are much less exciting and frequent in the winter. In addition, it is REALLY cold out on the water in winter. Instead of whale watching in the winter, consider a visit to the Whales of Iceland museum near the harbour. There you can see dozens of life-size models of these magnificent creatures.
If you book directly with Special Tours, use the discount code "GUNNAR" for 10% off.