More Culture than Race although certain genetic traits and diseases are currently being unveiled in supposedly Celtic populations in Scotland and Ireland. Possibly African in origin, currently being traced through Basque populations as previously mentioned. Based on a seafaring culture predating but eventually surpassed by the Nordics.
Celtic art and technology was sought after in the ancient world and much romanticized in 19th century England. Celtic technology included the first use of suspension in war chariots and the introduction of chain-mail to Britain and consequently mainland Europe. Some Celtic & Nordic artwork is undoubtedly responsible for the "Atlantean Myth".
Celts were indisputably fearsome and effective in battle but often disorganized when routed. The Romans had mixed success, the Vikings did much better.
It is a myth there are no Celtic peoples left in England, Cornwall for example is full of families tracing their roots back to Post-Roman times. The most interesting modern Celtic societies surviving are in the Hebrides and The Faroe's. The latter is a mix of Viking and Celtic cultures.
Celtic military technology and staff were actually quite dominant in Dark age Europe well after the Vikings had left the scene. But that is another story, search Gallowglass.
That insane Australian sun is too much for this little Black Celt.