That being said, the language barrier is still keeping many classical music fans, including me, from fully appreciating the art of opera. Attending opera performances, watching operas in DVD/Blue-ray with subtitles, or at least listening to recordings with a libretto at hand seem to be required for understand the medium, so we cannot listen to operas while reading or rearranging furniture. Before I can find more time to dig into operas, I listen to operas without words occasionally, simply because there are some of the best orchestral music ever written among them.
Here's the Spotify playlist: Opera Without Words (311 tracks, total time: 22 hours) Highlights including Tannhäuser Without Words - A symphonic synthesis by Lorin Maazel, String Quartet version of Mozart's Don Giovanni, and Arturo Toscanini's rehearsal of Die Walküre without singers. It may work better in Album view.
I also included some arrangements of famous lieder cycles. The difference with Liszt's piano transcriptions is here an instrument, other than the piano, sings the vocal part. Try this playlist if you fancy hearing a cello singing Schubert's Winterreise or a viola singing Schumann's Dichterliebe.