Many people consider St. Pölten to be a city of low touristic interest. Anyway its high living standard and the convenient location make it a place worthwhile to hang out some time and relax, e. g. at the lakes or to undertake some day trips. First impressions of the city and its surroundings can be found on the city's website (German).
St. Pölten is located on the Western Railway "Westbahn", one of Austrias main railway lines. You can take the High Speed Trains, which leave every 10 to 30 minutes from Vienna's Westbahnhof, some stop over in "Wien Hütteldorf" too, and it takes you about about 30 minutes to get there. St. Pölten is the terminus for the suburban train service from Vienna's Westbahnhof to St. Pölten too. It leaves Westbahnhof hourly and takes 80 minutes to reach St. Pölten. Tickets for both services cost 11EUR, or Vienna's VOR travelcards can also be used.
Viehofner Seen - The Lakes
These lakes are the remainders of an abandoned gravel mine. As there exists suitable infrastructure (public transport, pubs) it is a nice place to hang out. Also see: Viehofner Seen (German).
Wochenmarkt at Domplatz - The Weekly Market
This is the place where to by local food directly from the producers. It is also possible to by flowers and specialties, such as local sweets. Visiting the market is a nice activity perfectly combined with spending some time in the near located streetgardens.
Market Opening Hours: all year round with varying activity each Thursday and Saturday from 07:00 to 12:30
Klangturm - Tower of Sounds
This is a nice place to get a view of the city from above. Sometimes there are exhibitions in the so called "Klangkugeln" (sound spheres) which are worth a visit.
Opening Hours: all year round; Monday to Saturday from 08:00 to 18:00 and Sunday from 09:00 to 17:00; admission free! Also see: Website of the Location (German)
Go to Mariazell using the Mariazeller Bahn. The trip of 85km takes about 2.5hrs. This route is not only one of the first in Austria to become fully electrified (in 1911), some of the train engines from that time are still in operation (this is a world record). Beside of the impressive scenery, the tracks' arrangement is pretty ingenious because of the vast differences in altitude that have to be overcome.
When buying a ticket check if the train engines are of type "1099", which are the world record ones, so that you know the true promise of the Mariazeller Bahn.