The question is, what is aesthetically beautiful ?
For me its a Cabinet, that looks for example in the color of the wall behind it, with an clean matt finished paint.
I dont like premade subs, specially with electronics inside. So,i would always go the DIY route with normal MDF,
maybe round up the edges, build an flat cabinet and youve an slim looking box. For example with this scanspeak driver on the picture,
you can build cabinets with only 14cm depth. When a short depth + wallpaint finish is not aesthetically, then i dont know.
With an Fabric Cover even more or just turn the sub so the drivers facing to the wall, or what is even better,
build an Bafflewall, place the subwoofer (best way is of course an double bass array) and cover everything with Fabric.
Then use some compact speakers in front of it and when you showcase the system - you get fullrange sound what nobody will expect.
Subwoofer by FM Audio (Germany)
Subwoofer by Speaker Base (Germany)