Mit seiner Fülle von Informationen und Attraktionen ist ein Freilichtmuseum ein für alle Altersklassen geeigneter Tagesausflug mit pädagogischem Hintergedanken für die ganze Familie, der sich zum Beispiel in den Schulferien anbietet.
Using the ideas in this post, I got the answer that "für alle Altersklassen" is an adverb, and in another, that it is actually an "attribute" of the adjective "geeigneter".
Are both correct? if so, how do they relate to each other exactly?
Both are correct points of view, but it should be noted that adverbial instead of adverb is the right word. Adverb is a word class/part of speech, while adverbial is a syntactical function. So "für alle Altersklassen" is either an adverbial in the participle clause of "geeigneter" or an attribute of the adjective "geeigneter".
The reason you have these two points of view lies in the nature of participles, which are like a mix of adjectives and verbs. They describe nouns like adjectives, but can have objects like verbs. So you can see "geeigneter" either as something more verb-like, and "für alle Altersklassen" as an adverbial, or as something more adjective-like, and "für alle Altersklassen" as an attribute. It changes nothing in the meaning and the dependency structure, it's just a different way to describe the same thing.
It is also not true that adjectives don't have such attributes, e.g. one could say
Eine für alle Altersgruppen erfreuliche Nachricht.
And "erfreulich" is not a participle.
