2 of 2 Added contribution by Rick James

You must use WHERE (metakey, metaval) IN ( (4, 5), (5, 3) ). (4, 5) value combination means "country data (4)" = "country_id = 5", and (5, 3) means "theme data (5)" = "theme_id = 3".

This allows to select tour_id values matched at least one of this conditions. But then you must group by tour_id, count distinct (metakey, metaval) pairs for each tour, and filter only those tours which shows this count equal to 2 (condition pairs count).

Obtaining tour_id you can obtain whole tour record from tours table. - Akina

If you don't have at least version 5.7.3, don't use "row constructors"; they are grossly inefficient. – Rick James