Don (coral blue) 1997 by Don Brown.
Drifter (2008-2016, 2017) by Studio Drift. It's a floating piece of concrete. studiodrift.com
The Lost Pearl is a piece of art and a thing to play on. It’s designed by Madeleine Berkhemer, you can find it in The Park in Rotterdam (the Netherlands). google.nl/maps
Graft (2008-2009) by Roxy Paine (1966). Stainless steel and concrete. nga.gov
Four-Sided Pyramid (1997-99) by Sol Lewitt. nga.gov