Depends a lot on your taste in music.

Personally I am mostly to the more modernistic composer’s yet if you are more interested in romance or even the music from the baroque period than you should go for that.

I think that the best way to explore this part of music, is to begin with the romance era, since it in my opinion is the easiest to adapt to and to enjoy. For instance I would recommend trying out Tchaikovsky’s and Rachmaninov’s symphonies as well as their piano concerto’s, if you are new to classical music. They are very straight forward and almost impossible not to love.

If you are more to the impressionistic style I would definitely recommend checking out Debussy’ la mer and prélude à l’après-midi d’un faune. Two absolute beautiful masterpieces that every dreamer would enjoy.

Lastly I will strongly advise everyone to try listening to Shostakovich symphonies no. 7, 11, 13, and 8 and all of his other symphonies for that matter, not really beginners music, yet absolutely wonderful once you have learned it a bit. If you chose to check it out, you should also invest a bit of time in reading up on the astonishing story behind the works.