I am signed up for my 10th ABD as a solo traveler this summer (Iceland)! It's a fabulous way to travel as a solo! But yes, there is a 40% single supplement that you have to pay on top of the regular per person price.
If you're looking at the River Cruises, the single supplement is, unfortunately, 100%. You pay the same amount as 2 people in a cabin. It really sucks. The only way I was able to afford it was because they had a promotion for a 50% single supplement when they introduced them.
Let me know if you have any questions about doing ABD as a solo. I'd be happy to answer!
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