Suggested day-trip: Secret Lagoon
A popular destination for day-trips from Reykjavík is the area in South-Iceland around Geysir. Many visitors embark on the journey known as the "Golden Circle", which includes stops at Þingvellir National Park, Geysir and Gullfoss Waterfall. Nearby is Langjökull glacier, where tour guides offer hiking trips and snowmobiling. The third most popular attraction of the area is the Icelandic horse: there are many horse farms to found in the south, some who operate rentals.
Wherever you decide to go and whatever you decide to do, we suggest you end your day by relaxing in Gamla laugin or "The Secret Lagoon". Located in Flúðir, this geothermal pool is surrounded by small springs of hot water as well as "Little Geysir" which erupted every 5 minutes or so. The pool was built in 1891 and in 2005 it was restored to its original glory. The water is 38-40° c. warm (that's 100-104 Fahrenheit), so it's nice and cosy whatever the weather is. Despite its authentic feeling, the dressing rooms offer all of the modern-day comforts. Booking is advised.
At our marketplace, you can find some great day-tours including a stop in "The Secret Lagoon".