It's in Slovenia. "It shows that wooden wheels appeared almost simultaneously
in Mesopotamia and Europe."
"Present-day Slovenia has been inhabited since prehistoric times, and there is evidence
of human habitation from around 250,000 years ago."
"A pierced cave bear bone, dating from 43100 ± 700 BP, found in 1995 in Divje Babe
cave near Cerkno, is possibly the oldest musical instrument discovered in the world.
In the 1920s and 1930s, artifacts belonging to the Cro-Magnon such as pierced bones,
bone points, and needle were found by archaeologist Srečko Brodar in Potok Cave."
"The Ljubljana Marshes Wheel is a wooden wheel that was found in the
Ljubljana Marshes some 20 kilometres (12 mi) south of Ljubljana, the capital of
Slovenia, in 2002. Radiocarbon dating, performed in the VERA laboratory
(Vienna Environmental Research Accelerator) in Vienna, showed that it is approximately
5,150 years old, which makes it the oldest wooden wheel yet discovered.
It was discovered by a team of Slovene archeologists from the Ljubljana Institute of
Archaeology, a part of the Research Center at the Slovene Academy of Arts and Sciences,
under the guidance of Anton Velušček."