Water is an ever present feature within courtyards, whether for practical
purposes of gathering and protecting water in a dry climate, or for the
nurturing sound of water falling.
It could be a traditional fountain...
Source: www.water-fountains-plus.com
...a Solar fountain...
Source: www.prosperityfountain.com
...or even a fountain-looking sculpture without water:

Source: www.theguys.org
"A year in the life of a Czech Plush Monkey"
Such as this Mexican stone basin...
Source: www.mexicanstyle.com
...or this birdbath in a quiet church courtyard.

Sitting can be on chairs...
...or, on an organic form:

The "Council Circle" at the Sanctuary Garden at the Crossings, Austin, Texas.

Designs can be created by
imbedding stones into
concrete.
Asante design in the city of Kumasi,
Ghana, 1817

Patterns in cobbles at the Villa Gamberaia,
Florence, Italy.
From: "The Book of Garden Ornament"
edited by Peter Hunt
Patterns can be stamped
into concrete.

Here, a community of people work on a
mural for a Gardens for Humanity project.
Sedona, Arizona

Detail of a mural, one of many projects created by
Gardens for Humanity.
Source: http://www.gardensforhumanity.org/
Recycled objects, broken tiles and plates, almost anything can create a mosaic surface.

This mosaic wall was created by Antonio Gaudi (1852 - 1926). Gaudi was a Spanish Catalan
architect famous for his unique style and highly individualistic designs.

San Miguel de Allende, Mexico. Here the use of stone, brick, cut tiles and stone sculpture
make up this wall. Photo by Clara Cohan
Anything goes? Creatively, yes. What needs to be considered since the
sculpture(s) will be exposed to weather and possibly climbed on...
the materials must be durable and safe. Other than that,
the sculpture added to the courtyard must "fit" the overall purpose
or theme.

The sculpture could be a functional
work of art, as is this fountain.
source: www.acsgarden.com

A sculpture could be used to divide
up the spacewithin the courtyard.
German artist, Jorg Siegele, createde this piece for the Sculpture garden at the
Katitche Point Guesthouse, Virgin Gorda, in the Caribbean.

View through Bottle Gate into Sun Garden,
The Abby Aldrich Rockefeller Garden, Maine.
Photo by Alan Ward

...as did Nek Chand with his Monkey theme.
Source: www.inpreparation.com/ nekchand/gallery.html