Revisited Hveragerði today, in order to visit some new areas and the revisit the activity there. The weather cooperated, as it wasn't too windy, there was no rain, and the sun even came out for a while, allowing for a backlit eruption video.
Found the locations of Grýla and Leppaluði, a couple of boreholes which erupted years ago. Grýla has its own little turnout along the road with a warning sign, even though it was overgrown and not at all steaming, and obviously not active in a long time. A 5cm wide hole in a rock, years ago it could be induced to erupt up to 10m high. Leppaluði is a circular concrete platform about 5m across that has been filled in, and also does not steam. But between it and the river was a small area of what appeared to be sinter gravel.
Farther north along the road is the Gufudalur golf course. Up on the hillside are several areas of thermal activity. In a ravine just outside are a couple of mudpot like features. In the course itself, between a couple of the hole is a thermal pond in which there was a spouter active. There's a sign, "Fallreitur" in front of it, which may be the name, or a warning for golfers. This feature really can only be see on the uphill side, and consists of an opening in a pennisula in the pond. Nearby were a couple of other muddy vents. (It seems this course and Arikikapakapa in Rotorua are the only courses with geothermal hazards.)
Farther up the hillside were another fairly dry mudpot and an old wellhead steaming away. I could not find the features Dirk Niermann calls "Lava Pool" and "Rey-8" and "Rey-9". Also did not try to locate Littli Geyser or Gosi I and II, as I couldn't find good descriptions of their locations. Seems Littli was up near the Agricultural Station we passed by on the way to hillside features the last visit.
We also revisited the Hveragerði Geothermal Park, mostly to see the eruptions of Eilifur Goshver/Eternal Geyser. This feature was nice an regular while we were there, with intervals within a few seconds of 20m15s. A quick burst of steam to 10 meters, but quite entertaining. The pool near the entrance also became active with eruptions when I was able to observe it.
There are reports of this feature only becoming active around 2016, and on the Apple Maps satellite view, there's a suspicious rectangular object located at that location. These satellite maps are several years old, based on the various new roads missing on them. The Google Maps satellite view shows a steaming area.