They didn't dig 2400m 'deep'. They dug into the sides of mountains which rise 2400m upwards from where they dug, as a side a effect from a construction site for water tunnels and their access-ways which would have been dug anyways for the adjacent dam and electricity generation site.
AFAIK nobody goes 'that deep' for science alone, it's always adjacent to mining, leftofer/unused/abandoned tunnels, and often closes down when the mining ceases, and the operation getting too expensive without the ongoing mining.
AFAIK nobody goes 'that deep' for science alone, it's always adjacent to mining, leftofer/unused/abandoned tunnels, and often closes down when the mining ceases, and the operation getting too expensive without the ongoing mining.
See https://en.wikipedia.org/wiki/SNOLAB , https://en.wikipedia.org/wiki/Canfranc_Underground_Laborator... , https://en.wikipedia.org/wiki/Sanford_Underground_Research_F... for some examples.