The Wikitravel article for Rio de Janeiro, recommends a 20-30 minutes trekking trail to access the Sugar Loaf for free. Is it safe?
I'll answer my own question after staying in Rio and doing the trekking.
This trail is completly safe in all sense. There are police controls in the first part of the trail (the Pista Cláudio Coutinho) and in the upper part (the cable-car station). In reality, all the area is a militar settlement, so I doubt that anybody try to attack you there.
In the other hand, the trail is not so difficult as the video posted by @DarkLightA shows. Nowadays there are no need of ropes or similar to climb and the main problem is the mud if the previous day has rained (slipper danger).
We take more than a hour to arrive to the "top" so consider the wikitravel time estimation as very optimistic. Also the "top" is not the real top. There are 2 cable-car stations, the first one is where you can get by walking this trail, but the second one is the upper one (but the views are similar).
I've never been there myself, but I'll try to answer your question as well as I can.
There are several YouTube videos that give insight into the hike. Here's one: http://www.youtube.com/watch?v=97nw7rblN00
It appears to be very steep in some parts, with ropes built in to facilitate getting up. However, it is of course difficult to come to a conclusion based on a video.
Furthermore, there is a tour guide who has written about the place, and states:
"Without a doubt, you will feel safe when visiting Sugar Loaf. Not only the cable cars are new and well-maintained, but overall, the infrastructure of Urca Hill and Sugar Loaf (and its surrounding) are satisfying." (http://www.myriotravelguide.com/accidents-on-sugar-loaf-in-rio/)
In the post he is mostly talking about the cable cars, but here he appears to mention the surroundings too, which incorporates the hike up, I suppose.
There was one accident in 2008 with a group of climbers where one unfortunately died, but I believe this was sports climbers rather than hikers, who would have taken a more difficult route. A similar occurrence happened last December, again with a climber, not a hiker.
Overall it seems like it isn't much of a danger to hike up. However, a bit of common sense goes a long way. If you feel uncomfortable, just hike back down and take the cable car up. Better safe than sorry!
I am the founder of the website CitySafe which aims to assess the crime and safety levels of large cities and countries worldwide (it’s still work-in-progress, but so far I have done c. 40 cities and countries).
For my answer, I am referring to the page about [safety in Rio de Janeiro] (including a crime map).(FYI, Citysafe’s rating algorithm has assessed a safety level of 43% (100% being the safest) to Rio, and 51% to Brazil.
As explained in the safety review of Brazil, the country has some unsolved issues with crime; and Rio is no exception. Although the crime rates has been greatly reduced since the 90’s, safety is still a major concern in some parts of the city: some areas are very dangerous for travelers at all times of the day, while central areas tend to be safe during the day and much more dangerous at night. Rio’s Central Business district is the cultural and economic center of the city, home to arts and history museums, cultural centers, churches and shopping malls. Lapa, south of the Centro, is the city’s most lively neighborhood: the former red-light district is now an area dedicated to caipirinha in one of the many bars, listening to live samba and Bossa Nova under the famous Archos de Lapa (an old Aqueduct).
Santa Teresa is a picturesque neighborhood located on a hill, home to many artists and musicians, as well as the famous colored stairs “Escadaria Selaron”. During the day, the Centro area is crowded and safe – though there can be pickpockets, but there is a police presence. It becomes empty and thus dangerous at night, and on sundays when all the shops are closed. Lapa is very lively during weekends, but muggings are not unheard of. Stick to the center of the neighborhood and do not take any valuables. Santa Teresa is considered dangerous at night, since it is surrounded by 3 favelas. Do not venture there alone, and prefer using taxis rather than walking.
These neighborhoods are reasonably safe, although as a touristic place it attracts a whole lot of pickpockets and scammers. If you go to the beach, be EXTREMELY careful: there are many thieves who excel at stealing your belongings. Only take the minimum amount of money and personal items, and of course never leave them unattended. It is dangerous to walk on the beaches at night, and even Cariocas don’t do it.
To view the map of dangerous areas in rio, check citySafe