We parked up at the Dinas Rock car park and it was free. If you wish to do the shorter route, you can park at other car parks that are closer (there are several) the main one being Gwaun Hepste pay and display charging £6 per car.
Varied terrain which you would expect due to all of the waterfalls. There is a shorter version of this walk you can do which is approximately 7KM but we wanted to get all of the waterfalls in so made it longer and covered 17KM. All the footpaths are very well signposted and laid out and map boards are available all around the area to keep you on track.
This is a very busy walking area so although there is waterfalls etc all over this route and they do have access for humans and dogs you do need to be cautious of other users of the trails etc and use your common sense.
Dotted across the whole walk and at every car park.
The Angel Inn in Glynneath is a must visit spot for a post walk pint, super dog friendly even hosting a dog menu, great beer, great atmosphere, large garden at the front and welcomes muddy boots and paws.
On the longer route that we took there were some quite steep sections which you wouldn't need to worry about when doing the shorter version. Plenty of off lead opportunities outside the busiest sections of the walk if you can trust your dog around the water, Riley tends to get in the water and refuse to come out so we had him on lead for a large chunk of the day otherwise it would have taken a year to get around. It is a super busy Brecon Beacons destination, be prepared for a lot of people in the main section of the walk but don't let this deter you from going, the waterfalls are beautiful and in particular Sgwd Yr Eira is the one where you can walk behind the waterfall, its quite the experience.
I would highly recommend you get there early in the day to avoid as many of the crowds as possible. The pictures of this walk really don't do the location justice, it's simply stunning and you can quote easily spend a whole day there pottering around from waterfall to waterfall. Pack yourself a picnic and find a nice spot.