While watching a documentary called La catedral de las 6 cuerdas: la guitarra clásica, I noticed an interesting old double-necked guitar. I don’t know when it was built, but maybe the 18th or 19th Century? It doesn’t look like a Baroque guitar.
Here’s the video. The guitar is shown in passing at around 4:29.
That part of the documentary looks like it’s at the Museu de la Música in Barcelona, but I didn’t see that specific guitar on their website.
Here’s a 17th Century double-necked guitar for comparison.
Image used under CC BY-SA 3.0 license.