Learn French: Les sensations du surf sont passionnantes à découvrir. - The sensations of surfing are thrilling to discover.

This ties directly into the current lesson! When a specific noun is the subject of the sentence (here, Les sensations), and the following infinitive describes an action done to that subject (you discover the sensations), we use à after the adjective. If we used an impersonal dummy subject like "It is...", we would use de instead: Il est passionnant de découvrir les sensations.

Why is it du surf and not just de surf?

Du is the mandatory contraction of de + le. In French, you generally need a definite article (le, la, les) when talking about a broad concept or sport. So, "the sensations of surfing" translates to de + le surf, which always merges into du surf.

Why does the adjective passionnantes end in -es?

In French, adjectives must agree in gender and number with the noun they describe. Here, it describes Les sensations, which is a feminine plural noun. We add an -e to the base adjective passionnant to make it feminine, and an -s to make it plural.

Is passionnantes a false friend here? Does it mean "passionate"?