Iceland is a fantastic country to visit over a long weekend because there is so much to see in such a short time. First let's orient ourselves with a map and all the sights that are possible to see in 4 days.
Arrive into Keflavik International Airport. I suggest arriving as early in the morning as possible so you have a full day to explore.
Pick up a rental car. I highly suggest driving yourself around Iceland - it is EXTREMELY easy to drive, the roads are paved and well maintained with clear signs everywhere. Plus you get to see the sights at your own pace instead of being rushed by a tour company.
Head to the Blue Lagoon - make sure you book ahead of time!
Full Blue Lagoon tips and things you MUST know before you go here.
After you are sufficiently relaxed from the Blue Lagoon make the drive out to Hotel Ranga. The drive will be a little under two hours and you will spend your first two nights here.
You can read my full review on Hotel Ranga here. But some things you should know: it is the only 4 star hotel in Iceland and I had a truly fantastic experience. I can't recommend them enough.
Have dinner at the hotel and after dinner make one last push to see one of the top waterfalls in Iceland: Seljalandsfoss.
The drive from Hotel Ranga to the waterfall is only around 20 minutes. Enjoy the waterfall with as few people as possible. It makes it so much better. You can walk all around the waterfall and even behind it. Bring a poncho, or waterproof jacket, you will get wet.
Arrange a tour in the morning to walk on Solheimajokull Glacier. I suggest the company Extreme Iceland - I have heard good things. Although the tour will be different, read about my experience walking on Vatnajokull Glacier here.
After the tour head head to Vik Beach. Road 215 is the turn off. You will see a large sign. The beach has many amazing sights like gorgeous black sand, caves to explore and strange geometric monuments.
After Vik Beach head back on the one towards Hotel Ranga. Not far from Vik Beach a large car park will be on your left, this is the stop for Solheimasandur Plane Wreck. Be aware that the hike to the wreck is 50 minutes EACH WAY. Although a long stop the hike is extremely flat with no elevation gain. You are basically walking over rocky gravel the whole way there. The end is a very cool US plane that crashed in the 70s. You can climb all over it and inside as well.
After the plane crash your last stop is Skogafoss. An AMAZING waterfall with viewpoints above and below the falls.
Return back to Hotel Ranga for a much deserved dinner and a relaxing dip in one of their Jacuzzi's.
Your last day will take you back to the Golden Circle.
Take the one back towards Reykjavik. Immediately after the town of Selfoss you will make a right onto road 35. The first stop is Kerid Crater; A 55-meter deep volcanic crater that is around 3000 years old. One of the few sights in Iceland that has an entrance fee. ($4) The crater now holds a lake. There is a walking trail around the top of the crater and to the base of the lake.
Continue down road 35 and next you will come upon Geysir; A geothermal field with tons of hot springs. The main draw is watching Stokkur shoot a tower of water and steam 30 meters into the air every 10(ish) minutes. The whole area has many smaller geysers and pools of mud bubbles to see.
This is also a great visitor center full of expensive food. It is still a nice place to relax and maybe grab an ice cream!
After Geysir you will make your way to the last stop on road 35: Gullfoss Waterfall.
Actually two separate waterfalls, saying Gullfoss is impressive is an understatement. There are various easy hiking paths to points on the falls and you can even walk the ledges between the upper and lower portion of the falls. Beware: you will get wet.
Your final stop of the day will take you the last portion of the Golden Circle: Þingvellir National Park.
Þingvellir (Thingvellir) is a historic site and national park in Iceland, east of Reykjavík. It's known for the Alþing (Althing), the site of Iceland's parliament from the 10th to 18th centuries. On the site are the Þingvellir Church and the ruins of old stone shelters. The park sits in a rift valley caused by the separation of 2 tectonic plates, with rocky cliffs and fissures like the huge Almannagjá fault.
Source: Thingvellir National Park Website
Diving in Iceland, and specifically in Þingvellir, is one of the most unique experiences in the world. Silfra is actually a crack between the North American and Eurasian continents, meaning that you dive or snorkel right where the continental plates meet and drift apart about 2 cm per year. Also it has some of the clearest water in the world with visibility up to 100 meters!! Definitely book ahead - this is a popular tour.
You can find more information on diving Silfra here.
After your last long day head back to a hotel in Reykjavik.
Today you will probably be leaving Iceland. Spend the morning (if you have time) walking around Reykjavik and taking in the largest city in Iceland. Head back to the airport (remember it is about an hour away from Reykjavik) return your car and think about all you saw in the last 3 days.
Extra days and Final Thoughts
Also, even if you are only going to be in Iceland for a short time I suggest getting my FULL guide to Iceland which includes so much more information. Find maps to secret hot pots I found, my Instagram tips for Iceland and so much more. Best of all it is COMPLETELY FREE.
Lastly, if you are renting a camper van and traveling Iceland on a budget check out that article here.
I hope that helps you plan your trip and remember if you have any questions do not be afraid to email me at firstname.lastname@example.org or leave a comment below.