Tsarichina Hole

Elisaveta Loginova’s book “Tsarichina: Fateful Contact”: https://kibea.net/book/2535

Tzvetko Kanev’s book “The Tsarichina Experience”: https://knizhen-pazar.net/books/search?author=%D0%A6%D0%B2%D0%B5%D1%82%D0%BA%D0%BE+%D0%9A%D1%8A%D0%BD%D0%B5%D0%B2&name=%D0%A4%D0%B5%D0%BD%D0%BE%D0%BC%D0%B5%D0%BD%D1%8A%D1%82+%D0%A6%D0%B0%D1%80%D0%B8%D1%87%D0%B8%D0%BD%D0%B0&search=1

Tsarichina Hole on Google Maps: https://goo.gl/maps/64NcSqNad2jXSYQL9

Bulgarian article and photos from the only journalist allowed to enter the Tsarichina site: https://www-bgnow-eu.translate.goog/news.php?cat=2&cp=3&newsid=150100&_x_tr_sch=http&_x_tr_sl=bg&_x_tr_tl=en&_x_tr_hl=en&_x_tr_pto=sc

Records of the Sofia Conference: https://web.archive.org/web/20071011110808/http:/ufonews.in:80/supporting_pages_2/support_4.htm

CIA FOIA Log mentioning Tsarichina: https://www.governmentattic.org/4docs/CIA-FOIA-Log_2008.pdf