Unreal scene in San Francisco on Tuesday morning ... a daredevil is climbing up the city's tallest skyscraper -- with no ropes or safety nets.
The urban climber began his ascent on the Salesforce Tower in the middle of downtown S.F. shortly after sunrise -- and as of this posting, he's nearly made it to the top of the 60-floor, 1,070-foot tall building.
Videos shot by bystanders outside of the building are breathtaking ... showing the guy scaling the structure seemingly without any issues at all.