This basalt cave is on the Hljodaklettar hiking trail in northern Iceland's Jokulsargljufur National Park. For those interested in a morning or afternoon hike that is very easy except for a few moderately difficult sections, this is a must-do hike. You can probably get to the hike using a regular car, but I wouldn't do it in anything less than a four-wheel drive vehicle because of its higher clearance.
You may need to review the large image to see the rain. Though my wife and I spent the entire day hiking in a slight rain, which of course is not ideal for most landscape photography, it might have been our most enjoyable day overall.
C&C encouraged!
EDIT: Thanks to Allan for suggesting that I open up the details in the mouth of the cave. See the before and after images below.
Before Allan's suggestion:
After Allan's suggestion: