Learn Icelandic: Sundið er skemmtilegt.

In Icelandic, when you talk about general concepts, activities, or sports as the subject of a sentence, you usually add the definite article (the attached ending that means the). That is why the English phrase swimming is fun translates literally to the swimming is fun.

Why does the adjective skemmtilegt end in a t?

Adjectives in Icelandic change their endings to match the gender of the noun they describe. The noun sund is a neuter word, so the dictionary form of the adjective (skemmtilegur) drops its masculine ending and takes the neuter -t ending instead.

Can sund also mean swimming pool?

No, sund only refers to the act of swimming or a swim. If you want to talk about a swimming pool, you need to use the word sundlaug. To say the swimming pool is fun, you would say sundlaugin er skemmtileg.