Thanks everybody.
Here are four more.
1. The wood bridge on the brand new Ring Road, intended to protect the highway from floods from volcanic eruptions under Vatnajökull glacier. I believe the bridge was washed away a couple of years later. I also think this is about where Jökulsárlón is now, though it wasn't yet a lake in 1974, and doesn't show on our 1974 tourist map. That the bridge is wooden is strange, as there are no Icelandic trees big enough to provide the lumber, which must have been imported.
2. A modest hydroelectric plant, near Skaftafell.
3. The summit of Mount Hekla, several years before and after eruptions, which were then occurring about every ten years.
4. An abandoned sod farm in the north.