Probably Baltusrol. Our CEO was a member and invited all of us on the management team to play. Played the upper course the week after the 2000 US Amateur, so conditions were still somewhat tournament tough. I was about a 15-16 hdcp at the time and shot a 99.
The year after, played Ko'olau in Oahu, which at that time was the most difficult course in the US, with a slope of 157. It was target golf and felt like someone carved a course out of Jurassic Park. If you were off the fairway, you were in jungle. Sadly, the owners closed it in 2020 due to the pandemic and sold to real estate developers, so it no longer exists.
I was very fortunate having been in the convention industry for many years, and had the opportunity to play a lot of top courses in the US and Canada courtesy of tourism execs who wanted to show off their cities. I think at one point I'd played like 13 or 15 of Golf Digest's top 100. Also got to play St. Andrews, which, if you're really any good, might not be all that tough. But they ask that you're at least a 15 hdcp to play, and if there's weather, well, you're probably screwed as I was on that day, shooting 115. But I did par the 18th in front of a crowd.