The pedestrian tunnel is very intresting if you want to escape from the crowded city on the right bank. You can go by foot to the left bank and enjoy the open space of the left bank. On the left bank is also a beach and an open air swimming pool. Also great to have a drink in one of the cafes or restaurants.
When travelling from one side of the river to the other side it is a nice idea to take the pedestrian tunnel. (Which you can also take by bicycle)
The wooden escalators are just worth the trip.
The tunnel is:
572 meters long
31.57 meters below the streetlevel
4.30 inside diameter
4.74 outside diameter
I was walking around Antwerp on foot - my itinerary was similar to walk through historic Antwerp described here. Strict historical downtown with the Cathedral and Town Hall is compact and in contrast to Brussels flat. Even from Centraal Station (railway station) located east of a centre/downtown you can take approx. 30 min. walk (alternative: subway/underground to Groenplaats).
The only inconvenience maybe the fact that the streets aren't straight and perpendicular one to each other, so it's easy to get lost unless you have detailed map in your hands. You can always look up and find out the top of cathedral tower which is 123 m (403.5 ft) high and well seen from almost every place or ask friendly natives - they usually can speak both English and French.
Klapdorp is one of my favorite streets. It leads north from the town square / shopping district and bends east back towards the Central train station (sort of). Both sides of the street have small shops and restaurants. Often busy with pedestrians, the crowds lessen when you begin to encounter residential buildings and the occasional church. This street, more than any other has caused me to become lost in Antwerp. Note the deceptively gentle curve of the road and the four story buildings crowding the sidewalk. With an overcast sky, it’s easy to get turned around and pointed in the wrong direction. A wonderful street to explore, but carry a map to help find your way back.
At first sight it is very diffcult to get from one side of the river Schelde to the other side. Where are all the bridges? Well, there aren't any. But there are a couple of tunnels. One of them is the St Anna Tunnel, a tunnel for pedestrians. You can go down underground with an escalator and then walk for about 500 metres to get to the otherside.
The tunnel was built in 1933, in 1997 it became a protected monument.
You should definitely get around on foot. It's the easiest and nicest way to explore the city. If you don't like the short walk from the Central Station to the Meir and/or Groenplaats, you could take the underground. But after a long train- or car ride, wouldn't you prefer some fresh air?
Cycling is a possibility too, but on the Meir you may just as well step off your bike, as the pedestrians are not going to give way to you!
When around the river 'Schelde', one must definitely walk through this monumental tunnel. The tunnel dates from the early 20th century and is reachable by wooden escalators! A must see!