Across the street from the geyser field, you'll find a hotel with a gift shop as well as the Geysisstofa (geysircenter.com), which has an earthquake simulator and an audio-video show that explains the geological wonders of Iceland.
I grabbed a snack at the cafeteria, browsed through the expensive items at the gift shop and escaped the cold rain that picked up as we were observing the geyser eruptions.