This is one of the more technically difficult trails, but it will take you from Malá studená dolina to Veľká studená dolina, two big and beautiful mountain valleys, by climbing the narrow pass that connects the two (Priečne sedlo 2352m).
This is one of the more technically difficult trails and it takes a full day, so unless you're experienced you might want to warm up trying something easier the first day or two of your stay. Note that a part of the trail involves climbing (you don't need any special equipment, there are chains installed), so if you don't like heights it might not be for you. You will need good walking shoes as much of the terrain is rocky. Also, you should be prepared for any kind of weather, as the weather, especially this high up in the mountains can be treacherous. You can see and encounter patches of snow even in summer.
The trail begins and ends in Starý Smokovec, near the cable car station, which can be easily accessed either by car or the High Tatras tram.
This trail begins in 1 Starý Smokovec, where you can either hike up to 1 Hrebienok (45min) or take the cable car up. There is a marked trail going up, but it's quicker and easier just to follow the cable car tracks. From Hrebienok, continue along the red trail to 1 Zamkovského chata. You can also take a detour along the green (then blue) trail and see the 1 waterfalls of Studenovodský potok (creek) along the way (this will set you back about 20min). Both trails will cross at a bridge across the creek, either way you choose follow the red trail from there to Zamkovského chata.
Once you reach Zamkovského chata, you leave the red trail and follow the green trail up to 2 Teryho chata. It will climb steadily, and the forest will quickly change to dwarf-pine undergrowth. Eventually, you will reach a big zig-zag style climb just under the Teryho chata, arguably the most sternous along the route. This is when the terrain changes to rock/alpine meadow. When you reach Teryho chata, congratulations, the worst climb is over, and it should be about the time for lunch. Pop into the cottage for a drink and a hot lunch at a reasonable price, and sit back and enjoy the view.
Once properly rested, continue up along the green trail. It will start with another (smaller) climb, then plateau. Continue until you reach the green/yellow intersection, where you switch to the yellow trail. Continue a bit further, until you come to the bottom of the pass, where the chains start. Up from here it is a climb up the rockface. While chains make this easier, this is the technically most difficult part of the trail and will take 30-45min to climb, so rest before you start as there won't be an opportunity to do so later. Once you reach the narrow saddle (2 Priečne sedlo), you will be treated to some spectacular views of the two valleys below.
From here, you are going steadily down. Here, the colour marking of the trail disappears for a bit, so follow the small pyramids of rocks that are used to mark the trail in the rocky terrain (this is very straightforward). Along the way you will pass several mountain lakes and finally reach the 3 Zbojnícka chata. From there, follow the blue trail down along the winding valley. On the intersection with red, follow this to Hrebienok. Once again, you can choose to walk down, or take the cable car.
The biggest safety hazard along the way is the nature. Take proper hiking equipment and stay aware of the weather conditions. Never hike alone.
From Zbojnicka chata, it is possible to continue further via 3 Prielom saddle, usually to 4 Poľský hrebeň and back to Starý Smokovec. This whole three-valleys trip normally takes approx. 10 hours of straight walking. Including the resting time and occasional congestion at the saddles, you should get up early to make this whole hike in a day.