What are some really interesting things that the US government has declassified?

For instance, back in the 1970s, the government declassified the fact that the allies had completely broken the German ENIGMA cipher codes and were decoding and reading those messages so fast that they sometimes saw them before the Germans. Back in the 1990s, the US declassified the VENONA Project, in which they were often reading coded Soviet messages to and from their agents in the US. It confirmed what Senator Joe McCarthy had said back in the 50s and 60s, that Soviet spying was rampant in the USA and that there were many Soviet agents in US government than was widely believed.