It's not tourism based as such, the town is a regional centre for retail etc with people coming from nearby towns and cities for day trips to spend their money and there are people coming from further afield in the UK for weekend breaks etc and a programme of various festivals and events through the summer months to attract those weekend visitors. In terms of international tourists there is a steady trickle of folks passing through the town for a day or two while touring the UK and in the summer you get groups of French and Spanish schoolkids coming on educational trips but nothing major.
The economy is largely service based, there are the usual professional things you get everywhere like healthcare, education (a new university was founded a couple of years ago but it's very small at the moment, and there is a very expensive private school which attracts students from all around the world), lawyers, real estate etc. The town has never had any heavy industry like steelworks, mines and so on but there is a tradition of light engineering/machine tools type stuff. Caterpillar has a remanufacturing plant here, I think their business includes servicing and rebuilding tank engines for the Swedish military.
then there are a couple of automotive component plants and there's a plant of Doncasters Airmotive which services and repairs aerospace components.
Plus various small manufacturing and service industry businesses and some people also commute out to other towns and cities or have jobs that are partially home-based and partially out on the road around the country. And also the local government for the county is mostly based here so that's another chunk of the workforce.
Unemployment is low, well under the national average, but because of the lack of big companies in high-pay sectors like finance average salaries are also a bit below the national average. But then the cost of living, especially housing, is also a lot cheaper than areas with higher salaries like London and SE England to make up for that.