Here are some pictures we’re collecting from visitor accounts of visiting Thingvellir:
These photos from Angeline Kwan: (captions added by editor)

Overlooking Thingveller and Vallavatn, Iceland's largest natural lake

Thingvellir - one of many cracks or faults from volcanic activity

Thingvellir pedestrian walkway - despite signs, it's a historic tradition to wish for luck while tossing in coins.

Thingvellir - coins in clear water