the facility also has an informative website: https://grimeton.org/
and if you can't make it out to Sweden, there are virtual tours available: https://alexander.n.se/en/virtual-visit-to-saq-grimeton/
for further reading, here's a useful paper. https://www.navy-radio.com/xmtrs/vlf/alexanderson-mayes-1975.pdf
and if you can't make it out to Sweden, there are virtual tours available: https://alexander.n.se/en/virtual-visit-to-saq-grimeton/