Australia's most famous wine region. This is a great place for reds and in particular shiraz. Cycling between wineries is a good option. Barossa has a great cycling network and this is a fun way to spend a day or two. You can also take a tour with pick up/drop off in Adelaide. Some wineries charge for tasting.
A hop on, hop off service. They can do pick ups around the Barossa and Adelaide CBD. Adelaide pick up and drop off tickets are $60 on weekdays and $70 on weekends. If you are staying in the Barossa tickets are $45 on weekdays and $50 on the weekend. They also offer a similar service in McClaren Vale.