Seek out any Bach played by Glenn Gould. The incredible thing here is that Bach left sheet music but sheet music of the age did not include time, so the music has to be interpreted. The "Goldberg Variations" are this interpretation by Glenn Gould (a pianist).

I'd throw in Beethoven's 3rd and 5th Symphonies.

I'd also throw in something like Verdi's Rigoletto and Rossini's Barber of Seville.

In my past I owned a record label which specialised in pop, rock and folk music. I had to learn classical like I had to learn jazz. But the thing that made this easier for me was the realisation that there is far far more rock / pop than there is classical or jazz. It can be intimidating but you only need an entry point to get you started. Whatever that is will be personal to you, but the best advice anyone can give is to just listen.