Reykjavik is very walkable. Rather than paying for a guided walking or bus tour, I looked up attractions I wanted to hit, planned my own self-guided tour of the city and set out on foot.
It’s great exercise, you have the flexibility to stop and explore whenever you spot something cool and you won’t spend a dime on transportation. Keep in mind that the weather can be unpredictable, especially in the low season, so pack extra layers and an umbrella.
I will note that I was only in Reykjavik for one day. If you’re in town for a couple of days, it might be worth it to to buy the Reykjavik City Card, which will get you free unlimited travel by bus within the city. It also offers free entry into all of the swimming pools and a bunch of museums. You can buy a pass for 24 hours (about $35), 48 hours (about $47) or 72 hours (about $57).
Pro-tip: If you’re relying on your smartphone to navigate, add your destinations and create a walking route ahead of time when you have access to Wi-Fi. That way, you’ll be able to access your map on “airplane mode” and not have to pay for any international data.
Cost of transportation: $0