The £433m racetrack and leisure project aims to create 6,000 jobs in one of Wales' most deprived areas.
The bus station was demolished two years ago - before a deal on its replacement was finalised.
The public had been asked to stay away while firefighters damped down.
Warren Gatland's midweek squad have a chance to lift British and Irish Lions morale when they face the Hurricanes in Wellington.
Cardiff boss Neil Warnock says veteran striker Rickie Lambert is "unlikely" to get much game time in 2017-18.
South Wales Argus
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