Not all arched trellises need to allow people to walk under or through them. Metalwork arches that can be placed near a wall create the perfect place for climbing plants to twine. They can create seasonal shade without endangering the siding of your home. Ivy covered halls might sound romantic, but in reality, those little clinging tendrils set to work on destroying the surface on which they are climbing. A trellis helps prevent this damaging process.
Another idea is a window arch combined with a window box. It can create a beautiful shade for your windows in summer. Imagine a window box with morning glories climbing up the sides of the arch and perhaps colorful petunias growing in the bed below.