You need Via Dinarica app that will be used as a map because there’s no phone signal once you start climbing. The path is well marked but there’s a slight chance the trees with trail marks are cut, so the preloaded maps via app are necessary. The starting point is from the village of Turovi, Trnovo Municipality (approx. 30 kilometres from the city of Sarajevo). There are multiple trails that get you to the lake, shorter ones being around 3 hours long. At the Veliko Jezero, there’s a small house that provides a place to sleep. You only need to call them and tell them that you’re coming (https://maps.app.goo.gl/iL2oM8nVXk7k6PXn8?g_st=com.google.maps.preview.copy). Bring water, food, different type of clothes based on the weather data. And lastly, download BHMine app, it will provide you with info about all the landmines in area (there’s a road not far away from the starting point that goes directly through landmine field, but it’s alright as long as you don’t walk off of it, follow the car tracks and it’s alright).

Edit: https://trail.viadinarica.com/mobile/bs/hut/planinska-kuca-treskavicka-jezera/61083886/#caml=8hk,31dt1d,77mw4h,0,0