Sorry to contradict you, but here is no infinitive verb in this sentence. I think the confusion arises from the fact that in Dutch the gerund and the bare infinitive "overlap", so to speak: they are written the same, but we can know when it's a gerund and when it's a bare infinitive by looking at the context and the "role" they are playing in the sentence in which they are.
In this case, "naar de strand gaan..." can only be translated in English as "Going to the beach....", and in that specific context, both the -ing form in English and the -en form in Dutch are gerunds.
Hope this helps.
In Naar het strand gaan is leuk we have a complex sentence that if formed by two clauses:
√ a main clause (that is, by definition, independent), which in this case can be represented as *"X is leuk, where X represents the Subject of the sentence (here Naar het strand gaan*). As this sentence/clause is beginning with the Subject, we have Subject-Verb-Object word order.
Yes, I know, it doesn't look like it, probably you're annoyed at me. But bear with me and keep reading. If you can, try to get a sheet of paper to write down the sentence and analise it syntactically.
√ a subordinate clause (by definition, dependent, that it: if you walked into a room and said only that, people would expect you to continue speaking, your message would be incomplete), which in this particular sentence functions as the Subject of the whole sentence. This subordinate clause is here Naar het strand gaan.
Now, as this is a subordinate clause, the Verb (gaan, in this case) needs to be the last element in the clause (not in the sentence, careful there), therefore, as this clause has no Subject, because we are using a Gerund (and Gerunds are non finites, and non-finites cannot take a Subject because a Subject requires a finite verb), we need to place the Object before the Gerund.
I wish I could make you a representation here, but well...
Remember that Dutch is a V2 language, which means that the finite verb (that is, the conjugated verb) needs to be the second element in main clauses.
For studying Dutch and German it is vital to learn a bit of grammar (not spelling rules, eh? But syntax, word classes, grammatical functions and categories and, especially, the different types of clauses (main/independent and subordinate/dependent), as it's key when trying to understand the syntax (order of elements/constituents, wrongly called word order -not judging, though, since sadly this is mostly not taught at school or it's taught badly, with a behaviouristic approach, without stimulating students' critical thinking skills).
Sorry, I just love grammar. Anyway...
Hope this helps!