Know Before You Go
There are tours to the bunkers but they are also accessible by public transport or walking. Finding the bunkers is not always straightforward though, and it helps to have access to a phone or other device with GPS-enabled maps. Most of the bunkers are marked on Google Maps or the map on the Bunker BS-8 website. BS-8 (and nearby BS-9 and BS-7) are probably the easiest to get to and, for energetic visitors are a good starting point to work your way back to the city along the string of fortifications.
To get to BS-8 take the number 80 bus from Zochova stop near the old town and travel for 7 stops to Kopčianska street. Once you get off, walk further down Kopčianska street until you see the signs on the right that say "bunker." Do not take the advice of Google Maps in taking other buses such as the 91 or 191 and following alternative walking paths routes. They may not look it, but they are significantly more convoluted once you get off the bus. BS-8 can also be accessed by car directly from the Austrian side of the border.