Open days are often held at the very end of an excavation, so they're a bit tricky to try to time. There are a lot of great museums to get your archaeology fix though. There are also some shell midden sites in the Kanto area like Kasori that have cross sections exposed if they're a stratigraphy nerd

Shell missed are right up her alley (mid-Atlantic archaeology in the US), so I’ll look for those, thanks!