I think you already got many valuable hints above. Walking down Aradena is just great and once you get to Marmara you can eat-drink-swim and then take a taxi boat back to Loutro. You can call a taxi boat (I think there's a phone number on the right side of the beach) or ask in the taverna when does the next one come. There's not much you can do wrong once you got to the beach - taking a boat back home is the nicest option after walking.
However... you should carefully watch your steps and follow the signs (there are some) in order to stay on the trail running on the side of the gorge (the upper half of the walk). There are parts with some handtrail. You are not supposed to take the iron ladder. Otherwise you will need to seek your path to climb down multiple bigger rocks, these are kind of unsafe. (But I'm still not sure about what exactly you mean by dangerous).
Maybe you would like to check at least youtube for videos (there are so many of them...) - they really won't spoil the surprise of the real experience but you can make up your mind if you want to go.
Last but not least: take water with you, have a great time.
Last edited by Joanna
on 11 Jun 2016, 18:34, edited 1 time in total.