What a journey that has been

On https://www.nytimes.com/2022/01/24/science/james-webb-telescope-arrival.html from which it could spend as much as 20 years in surveillance of the cosmos. It traveled about a million miles since launching on Dec. 25, and what a journey that has been.

(NYT.)

Is the clause what a journey that has been an exclamative clause or interrogative content one in the sentence above?

And if it is an interrogative content clause, could it be a main clause at the same time?