Checked back this morning and they had one time slot available, so I was able to purchase my tickets.
Any other attractions you recommend I pre-purchase?
Whew. Yasher koach.
Looking back at my TR, I realize I never completed it. Add to my to-do list....
After the Sal Meijar Sandwich shop lunch, we went to the Rijksmuseum, which had no line and did not require advance ticket purchase. Nice stuff there, but I can't say it was a "must-do."
We then went to the Heineken experience. Had a terrific time. There was a line, but I was able to purchase my tickets online at that time, and then we were able to bypass the line, so no need to advance purchase.
We had a great time at the Heineken experience. I never really liked Heineken beer, but boy it sure tasted good there.