As an interior designer, I would suggest choosing something along the same genre as your castle. If it is of the Italian-style architecture, then you'd want to get something that is apropos of Italy, say an Italian villa or a vineyard in Tuscany, perhaps a tapestry with an Italian palazzo, piazza or gazebo. Or, if pictorial tapestries aren't your thing, try going with something geometric or abstract—even using an area rug for wall art works. Just take it to someone in the upholstery business who can fashion it into hanging art. You'll need to get it bound and have loops put on it to hang. Choose hardware (a.k.a. a hanging pole) that works with the Italian style, paying special attention to the style of the finial to bring out the style you're going for.
If Italian isn't your architectural style, take these tips and hone them to whatever style works with your place. If European in architecture (British manor house or French chateau, for instance), a good standby is a tapestry of a lovely still life of vivid flowers in a gorgeous urn-like vase. I just saw one recently in my catalog perusing that I thought was exquisite, but I don't know where you're writing from, so you may not be able attain the catalog where you are.
Another favorite would be of a cottage house along some babbling brook mingled into a thriving country garden and meadow scene or an outdoor café/bistro scene would work for either the European or Italian genres.
Not knowing much about you, your house or your tastes, it’s hard to really pinpoint any one particular work or style. Since you said your walls are white and that you have gold-leaf wood carvings, you’ll want to maintain a harmonious design scheme by choosing a tapestry and hardware of the same monetary caliber as your abode (i.e. an expensive, high-quality tapestry). Keeping the quality high will cost more, but it will work better with the overall expensive air of your place. Try to watch the scale of the tapestry you choose, too. Too small and your wall will engulf it, overpower it. Too big and it’ll engulf the wall.
As for the color scheme—assuming white and gold-leaf are all you have in the room—almost anything you choose color-wise will work out, whether it be floral, landscape, abstract or geometric. Just choose a tapestry style and colors that you love and can live with and you should do just fine.
Choosing new accessories for my rooms is always the best part of my decorating experience. I hope it will be for you, too. My best to you.
P.S.: I’ve listed some internet sites below that you might want to take a look at for ideas. Hope something pays off.
At the designtoscano.com site (letter B), under Tapestries, they have these categories:
Medieval & Renaissance
French & Italian
Finials & Rods & Tassels
I saw some really nice ones that appeal to my taste under “French & Italian” and “Florals.” Of course, our tastes probably differ. I generally go for the romantic, floral or landscape styles for my home. Hope this helps.
"Wide selection Italian/European/Belgian- Jacquard/Chenille tapestries, wall hangings, cushions, mats, throws, runners, handbags."
“Introduce the ancient art of wall hangings into your home. We offer only high-quality masterpieces selected from workshops still weaving using methods handed down for generations.”
"... Italian Made Tapestries. Italian Tapestries, let you own a piece of history by introducing the ... anyone to order high quality made-to-measure frames, at competitive prices. TAPESTRIES ..."