This itinerary is designed for the winter months (November- March). During this time daylight is limited so you have to make the most of the bright hours of the day.
It's also Northern Lights Season so keep an eye out for them. There's no place that is better than others to spot them, what matters is to have little light pollution around you and clear skies. If it's cloudy you can't see them. You also want a high KP forecast, ideally 3 or more. This is the site I use to see the forecast: https://en.vedur.is/weather/forecasts/aurora/
Start in Keflavik and make sure to get a 4x4 rental car. The weather this time of year can change quickly and snow is common so 4x4 drive is recommended.
On day 1, go explore the Golden Circle area. It's an easy to start to your trip with fun stops. There's lots of cafes on the way so you can eat whenever you're hungry.
Start the second day with a quick dip in Hrunalaug hot spring, then continue along the south coast and see all the amazing waterfalls. You'll be driving back the same way so you can save some for later if you like. Spend the night in Vik and don't miss out on Black Crust Pizzeria!
On day 3 it's glacier day. Go see the Glacier Lagoon, Diamond Beach and Svinafellsjökull. I recommed to have lunch at Fjallsarlon, they have a good restaurant.
My favorite Ice Cave in in Iceland is on the way home in Vik. Book with Katla Track and remember to use code "ASASTEINARS" for a discount.
Spend your last day exploring Reykjavik. If it's good weather I highly recommend to go whale watching with Special Tours. Use code "ASASTEINARS" for a discount.
Before you fly out, it's always a good idea to stop quick at Blue Lagoon on the way to the airport.
Enjoy your trip to Iceland! //Ása