Most people hike with a guide but you don't really need one. To go by yourself you need a permission from Conaf. Conaf is in the city center (open from Monday til Friday). You need to show them a kind of document that proves alpine experience (DAV membership for example in Germany). With that document you can rent gear (see photo) in town. I would highly recommend to rent thick waterproof trousers as well as you slide down the vulcanoes on your way back. But at some spots you can't use the Poporutscher (kind of sledge, you need to rent it as well), otherwise you would be too fast. You can get to the starting point by taxi, but some drivers will not go because it's too steep/only possible with a off-road car. So ask them beforehand. From my point of view the road is OK. You could also get a normal taxi to the park entrance (conaf station where you pay entrance fee and show your permission) and from there try to hitchhike. Try to be there before 7 (conaf was open beforehand even if...