Gio, 'aller' doesn't take the preposition 'à' before an infinitive (in most cases - see added information below), and 'est allé à visiter...' is not grammatically correct here.

In French, the translation of 'went to visit (somewhere)' is simply the past tense of aller, followed directly by the verb infinitive 'visiter'. 

English uses the preposition 'to' as part of the infinitive - 'to visit'. French does not use a preposition as part of an infinitive verb form. Whether 'à' or 'de', or no preposition, is needed depends on the preceding verb, not the following infinitive.

https://www.lawlessfrench.com/grammar/verbs-with-a/

Aller à is reserved for places: aller au cinéma, aller à Paris, etc. 

Aller + infinitive: aller visiter mes parents, aller faire du shopping, etc.

For completeness, there are many expressions that use ‘aller à….’, with various meanings, not restricted just to places. 

The list includes at least one fixed expression with an infinitive -“ aller à ravir (à quelqu’un) “, which derives from the expression “ aller à (quelqu’un) “.

The exceptions in French !

 Aller à = to suit someone (French Expressions with aller)

https://www.lawlessfrench.com/expressions/aller-expressions/

 https://www.wordreference.com/fren/aller%20à

Hi Maarten, thanks for that clarification. Of course you are correct. I was only thinking in the limited context of the question.