Submit your message on the future of communications or solar system exploration. It might be chosen for a time capsule aboard an asteroid sample return mission.
Tool marks within the engraving suggest that it was likely created by someone who intentionally passed a sharp object again and again over the cave wall.
The blue hour - when the sun is some distance below the horizon, when the sky is deep blue and the landscape is suffused with bluish light - is a good time to take photos.