Thanks all for the information.
A few more details - We are on 1 ticket with a long layover (not by choice). I haven't decided if we'll check bags or carryon. If we check, do we have to collect our bags to go through immigration and recheck to final destination? That's what happens when we land in the US if our first stop isn't home.
I saw the other posts, they were traveling outbound to non-Schengen flights and/or back to US. Since we are going to a Schengen country, and flying business class on Delta/KLM, how early should we be back to the airport? Hoping not the full 3 hours early. We will monitor the available links when we are there.
Hopefully flying business we will sleep and not have too much jet lag. That being said, we don't want to schedule anything that needs advance tickets in case travel plans go awry... no need to start vacation stressed to make an appointment! We enjoy history and experiencing the food and culture. Given the timing, I think a nice early dinner would be fun (gluten-free options). The canal boat tour also sounds interesting - are they readily available?
Thanks!