The Wien Mitte train station is the central hub connecting the train lines S-Bahn with a metro train system named U-Bahn. Look for U Bahn signs leading to the Landstrasse U-Bahn Station. Look for the ticketing machine to purchase the ticket. U-Bahn tickets are as follows: Day Ticket Vienna is valid on all public transport services in Vienna for one day from the started date until 1.00 am on the following day. (5.80 euros) 24-h Vienna ticket is valid on all public transport services in Vienna for 24 hours from the stated date and time. (8 euros) There are a variety of tickets, including the 48 and 72 hours tickets, weekly card and so else all are available at the ticketing machine.
Photo Von Gugerell - Eigenes Werk, CC0, https://commons.wikimedia.org/w/index.php?curid=26451702