Unlike the others, Heidelberg Castle is in ruins. For the post part I'll let the pictures speak for themselves, since there was too much detail to remember.
Afterwards our bus took us to the Frankfurt airport, where we had a 4 hour wait until our Finnair flight to Helsinki. The baggage drop-off wasn't going to open for two hours, so several of us found a bar and chatted to pass the time (I had a sprite and some water). Security was a little tighter than in some of the other airports on this trip but there seemed to have been a bit of randomness; only one of us had to have his shoes x-rayed.
The 2 hr 20 minute flight was uneventful. In Helsinki we took a Finnair bus that dropped people off at major bus stations, including one about 200 metres from my hotel. Let's hear it for city navigation apps! The other writer at the same hotel used Google Maps, but I didn't sign up for a data plan; I had an offline mapping app but didn't need to use it.
My hotel room at the Holiday Inn Exposition and Conference Centre. My noise sensitivity and consequent need to retreat from crowds constituted enough of a disability to get me a room in the conference hotel; most of the others are scattered across several hotels closer to the city centre.