Things to go in Goteborg?

Any particular eras of history you prefer? It's a young city, founded in the 1600s, so there is not a lot of ancient history. If you like the outdoors I can suggest a trip to the archipelago. At least if the weather is nice, September can be rainy. Where was your father an exchange student?

The southern archipelago (Brännö/Styrsö/Vrångö) is highly recommended and easy to reach by Bus 114 or Tram 11 from the city center (change to any chosen ferry for free at Saltholmen). The same ticket as when travelling solely in the center takes you all the way. Stroll through the Trädgårdsföreningen park or up Linnégatan to Slottsskogen park where moose and reindeer are kept. Have a look at the Domkyrkan church, which is quite unique considering that most other churches of this magnitude were built in other styles and other eras. It is a favourite building of mine. Have fika at Latterian, Caféva, Le Petit, Ahlströms or Brogyllen. Buy gelato at Råda Gelato or Gelaterian. Eat at the genuine Solrosen vegetarian taverna in Haga (fully liscensed), run by the same local for half a century.

Thanks!
We like prehistoric history which I realize is not here. And WWII.
Father in Law: Lived in Saro and school in Kingsbacka.
Thanks for the suggestions. I think we definitely want to do some exploring in the archipelago.

Särö and Kungsbacka are easy to reach, they are basically just suburbs. So need for extra planning to get there.

For prehistoric history I can recommend a visit to Tanumshede to the north and the Bronze age stone carvings there, a Unesco world heritage site.