To walk safely in this gorge you will need walking shoes with a reasonable grip. Do not ever walk in the gorge of Aradena when it is raining or has rained recently: the risk of stones falling is very real. On the subject of stones, there are a fair amount of goats in the gorge (no, they are not wild!) and these have a tendency to dislodge stones. Do not pass right under where there are goats. If you have no alternative way, wait till the goats have moved away and if necessary chase them away (by throwing stones at them, of course!).
First you need to get to the beach of Marmara. This is best done walking (in about an hour) along a coastal path from Loutro. Alternatively, in summer there is a small boat taking people from Loutro to Marmara at 11.00 am. Check in Loutro if it is running.
You cannot miss the start of the gorge. Just walk up following the path in the river bed. The beginning of the walk is between high cliffs so you will get a fair amount of shade. As often there are a lot of oleander bushes (they flower in May - June) in the river bed. Avoid touching them, they are poisonous and some people will develop allergic reactions from simple skin contact. After about 30 minutes walk, the gorge widens a little and you will see a sign pointing to the right with Taverna Livaniana written on it. This path takes you up to the village of Livaniana. An alternative if you just want a short walk through the gorge. Otherwise keep going straight up the gorge.
The path is marked with stone cairns and in places with spots of colour paint. Pay attention to them because there are several places where you might take the wrong route. You would not get lost but might make it a little bit more difficult. In a few spots there are two paths that have been marked. Don't panic, in this case both routes are OK.
I always compare the walk through Aradena to walking up a staircase with very wide steps: you walk for a while on almost flat ground, then get to a short steep part then flat again and on like this. There are seven steep passages. These are the parts where you are better off walking up (but still treading carefully) than down.
At the second steep place, in the middle of large oleander bushes there is a small spring, a little hidden from the path. This is the only water place in the gorge. This spring is really easy to miss (there are two paths that are marked with red dots and one of them does not pass near the spring) so do not rely on it for water and make sure that you carry enough for the whole walk.
After about one and a half to two hours you will arrive to a kind of fence across the gorge and have to turn left and start climbing a new path which was built to avoid the famous ladder which was used until then. It passes well above it, in the side of the cliff and descends again into the gorge. The path is well built and reasonably wide but you still need a little head for heights as it goes into the side of the cliff.
If you want to go the old way, pass under the fence and you will arrive to the metal ladder, in fact two of them within a couple of minutes. The higher one moves a little when you are on it but don't worry, it is really solid. After the ladder keep climbing up (it is a little tricky for a bit) until you reach the river bed again and soon you can see the bridge which leads from Anopolis to Aradena high above you.
You need to pass under the bridge (where you will often encounter rubbish and assorted nasties) and keep walking for another 10 minutes up the river bed. You then get to the very good path leading out of the gorge. If you go to your left it takes you to the village of Aradena, if you take the one leading up to the right (it starts about 40m further up the river bed) it takes you out on the other side of the gorge towards the village of Anopolis.
If you have never been to the village of Aradena, I would definitely recommend a visit. It will give you a good idea of traditional Cretan architecture. If you want to continue to Anopolis follow the road (going east! going west will get you to Agios Ioannis where the road ends) for about 30 minutes and you get to the village. If you need to carry on to Chora Sfakion (about 13 km by road) it is generally quite easy to hitch a lift.