From the dinant downtown you have two ways to reach the Citadelle 100 meters above the town: the first is on foot climbing 408 steps; the second is by cableway.
The entrance fees, incluse the entrance to the Citadelle is 7.5 Euro a adult.
The train ride from Namur to Dinant follows the Meuse River. The scenery along the way is very beautiful and all along the river there are large hills. Many of them are dotted with old of fortifications and stone walls.
Dinant is about an hour away from Brussels.
There are three ways to reach the fortress, the road which takes you up the back of the cliff, or you can climb up 420 steep steps from the front alternatively you can take the citadel cable car.
The cable car station is next to the Notre Dame Church in the main high street. I can not remember how much it was, not expensive though
Dinant is quite liveley and there was lot of traffic when we were there. It was a Sunday, I don't know if it's less busy during the week. So be be patient when driving there...
However we didn't have a problem to find a parking space. There are some public parking (not big, though) and you can also park your car in the streets (but use the marked areas). In the surrounding of the center with the church, you have to pay for the parking space, but if you have no problems to walk a bit, you will easily find a free parking! At least that's the situation on the same side of the river as the church is. It would be worth to look for a parking on the other side, too, especially as from there you'll get some nice sights on the church and the citadel!
And if you want to visit the citadel, you'll also find a parking up there.
Getting to Dinant by train is a lovely ride, if a challenge. Lying off a spur of the Brussels-Luxembourg line, Dinant requires a change of train in Namur, followed by a relaxing hour ride up the Meuse.
Visiting as a daytrip from Brussels is certainly possible (I did it that way), but to be honest, a trip to Dinant might be better suited to a weekend getaway in the Ardennes, along with Luxembourg and Namur. Just a thought. Regardless, you ought to visit -- it's such a cute little town.
Parking in Dinant can be quite an adventure. If you do not want to get stuck in the hectic traffic of the city centre, then it might be a good idea to park a bit before or after the Citadel.
When I was there, I parked close to the Casino, it was a free parking and I only had a 10 minutes walk to the Citadel.
Not many people will arrive in Dinant with this means of transport, but according to the boats laying at the kays ... it is a popular way of getting there (only for the slightly richer people).
Most other people will arrive in Dinant by car, which is no less spectacular as for the descend from the Ardennes into the Meuse valley. Parkingtip: on the opposit side of town, along the Meuse-kay ... even just sitting in your car will already have impressive effects.