Le chat est allé à un musée

Le chat est allé à un musée. Il s'est ennuyé énormément. // The cat went to museum. He was very bored.

We carry on with Passé Composé (and a few other things). Reflexive verbs take "être" as an auxiliary, and aller (to go) is one of the few non-reflexive verbs that also take être. So here it is used in both phrases.

We were given a table that explains when you use être and when avoir. I really like that fact that in the avoir section there is a box which simply stated "TOUS LES AUTRES VERBES", all the other verbs.

Rather reminds me of the alien vocabulary used in "Кин-дза-дза" movie which consists of a several special words and a catch-all word "КУ" (KOO) used for everything else.