Hello how may I help you? Can you tell me what the tallest building in Denver is? It;s the Republis Plaza Thank you. And what's the second tallest building? It;s the geary building How tall is the tallest building? The Republis Plaza is 250 ft tall. When was it built? it was built in 1950, Geary was the tallest building for nearlu 30 years *nearly OK, thank you. Welcome