One of the safest cliff spots for sure. Clear the high area of Cascades and you are good to go. The only people that have a clear line of sight on you are South from your position but this spot is very high so they will likely not notice you from far away.

To access this spot, you will need an Octane. Rougly place a Launch Pad where indicated in the screenshot below and super jump: press your jump key right after you hit the Launch Pad and be ready to air control and climb when you hit the cliff. Once you are there, you can lock yourself in the crouched position at several spots. Try to have all your team members at the same place so you are less likely to be noticed.

You have a great line of sight on all the teams coming from the South and you are completely covered from your North-East. If the last fight happens in front of you, it is a good idea to have sniper rifles in your team so you can even the fight between the other 2 teams. This will ensure the winning team is at their weakest when you go fight them.