Hike (6hrs), or not
There are two ways to get to Llaca Lake: hiking or driving with a short walk.
For the hike, take the No. 15 colectivo from Huaraz through Marian to Cachipampa. The drive should take 40 minutes. From there, the hike is about 3 hours. The map below shows the trail (in yellow) starting near Marian.
You can drive an hour and a half from Huaraz to the Llaca base camp, from which you can walk about 40 minutes to the mirador.