Gullfoss waterfalls are on what is known a Golden circle. One of the ways to get there is to take route 35 north just before route 1 reaches Arborg. This will take you past Geysir and to Gullfoss. There are also alternative roads, but unless you have a 4WD car, you best stick to the main roads.
Gullfoss waterfalls are one of the most famous waterfalls in Iceland. Three level falls attract a lot of visitors. And being located within a driving distance for one day tour out of Reykjavik makes it really popular. If you are hoping for a bit more space and some peace you need to come there outside of the normal tourist hours, meaning super early in the morning or later in the evening. In a summertime, sun is up for most of the 24 hours, giving you some extra time.