Prince Charles and his wife received a distinctly Kentucky welcome Friday during a visit to the Bluegrass state, where the royal couple got a glimpse into efforts to promote environmental sustainability and protect historic buildings — among the prince's favorite projects.

During a whirlwind visit to Louisville, Charles chatted with onlookers, attended panel discussions and called for fundamental changes toward a more sustainable economy in sync with the environment.

"If we wish to maintain our civilization, then we must look after the Earth," Charles said in a speech at the Cathedral of the Assumption. "In failing Earth, we are failing humanity."

Charles, next in line to the throne, said climate change threatens "to engulf us all."

"As a grandpa, I have no intention of failing mine or anyone else's grandchildren," he said.

Charles and his wife, Camilla, were serenaded by a choir singing "My Old Kentucky Home" at the start of their visit. They received a welcome from the city's most famous native son — boxing great Muhammad Ali — that was read by the city's mayor.

"As you travel back to your homeland, we hope you know how much this city respects and admires the many contributions you have made in the world," Ali wrote in the message read by Mayor Greg Fischer. "We think you are the greatest."

Charles watched as an employee for spirits maker Brown-Forman Corp. showed how whiskey barrels are made.

"He had a lot of questions about what the oak does to the product, and what creates the ... flavors that we have with our products," said the employee, Chad Ruch.

Greg Abernathy, assistant director of the Kentucky Natural Lands Trust, had a few moments with Charles to describe a project aimed at protecting a 125-mile-long forested corridor through a region that includes southeastern Kentucky.

Kentucky Gov. Steve Beshear said he hoped the royal couple's visit deepens ties between Kentucky and the United Kingdom.

Schoolchildren lined up outside the royal couple's event at the Kentucky Center for African American Heritage. Charles and Camilla shook hands and chatted with some of the youngsters.

Jailen Leavell, 15, was part of the River City Drum Corps that played for Charles and Camilla.

"This morning I just could not sleep," the teenager said. "I woke up at 4 o'clock just thinking how in the world was I going to handle this. Being able to actually see him is very surreal."

Charles attended a discussion on agriculture, visited with environmental activists and took a trip to the Old Louisville neighborhood, known for its stately Victorian homes.

Outside the cathedral, Charles shook hands with Scott Render, who was biking home from work.

"He said, 'I see you're getting some exercise. I'm very impressed,'" Render said.

The Kentucky stop concluded the royal couple's visit to the U.S., which included a visit to Washington, D.C.