Unique! However, there are a few things you should definitely know before booking (unfortunately I didn't find out about them until the bus was halfway to the Silfra fissure). There it was said that people with physical problems such as asthma need a medical certificate and their inhaler. But that was not checked. Putting on all the diving equipment when several groups arrive at the same time takes a lot of time and is a bit strenuous. Nothing for the particularly squeamish. We were annoyed by millions of small flies. Recommended: pack warm, comfortable long-sleeved and long-legged clothing. Valuables stay on the bus At the end you have to swim against a very slight current, which was a bit tiring due to the cold. Keeping your hands behind your back actually helps a lot against the cold on your hands