New York City
Going to Iceland the first week of October and only have 4 full days to explore. Thinking about renting a car but not sure of weather conditions if it'll be worth it or easier to do tours. Open to any helpful suggestions and anything that is must-see, must-eat, must-do etc. thank you!
A car isn't essential but exploring Iceland independently (or with a private tour, if you can afford it) will definitely allow you to see more of the country, to stop off at places where organised tours don't stop and to plot your route so you avoid the major sights & sites when the majority of tour buses are there. It will also allow you to visit some of the many other hot spring spas and thus avoid the usually-crowded, tourist-popular and expensive Blue Lagoon.
There are of course organised full-day tours which cover the primary 'must-sees' for many visitors:
There are plenty of other tours available, both small group and larger,, including activity tours and trips to less-visited areas. I suggest you browse through the tour options on this reliable and extremely useful site (and recommend you book through them too):
Make sure you allow at least half a day (and preferably a full day) to explore Reykjavik itself. It's a small city, easy to explore on foot and extremely safe to walk around. Don't miss the Saga Museum, Hallgrimskirka church,the Sun Voyager sculpture, the National Museum of Iceland and...if you allow a whole day...do take the bus (or drive, if you have a car) to Arbaer Open Air Museum just outside the city. The museum has 20 buildings and will give you an excellent idea of what Icelandic life was like in the past.
Lots more info on the official site here:
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Blue Lagoon, go in the morning and plan for half a day. Do the organized Golden Circle tour route... I don't think a car is necessary. Must eats- the hot dog stand down by the cruise port and the Chips place in the middle of downtown. I didn't get to do the diving tour but you can dive between the tectonic plates in winter which looks amazing.