Environment Design Problem

Environment Design Problem

I am searching for the best approach in level design. I know what I chose to approach in level design will finally effect gameplay and that is what I actually wanted to do. I want to ask some opinion from the creative mind in this forum. My question is which is better for gameplay for my third-person RPG game:

1. block the player progress by difference in player level and monster level. Player cannot progress because the monster is too high level for player so they need to level up first before they can clear the area. The level design for this approach will be more simple without any other thing that can block player from going anywhere except for the monster.

2. block the player using key and lock mechanic. Player need to find something or solve certain puzzle to unlock another area and continue with their journey. The environment design will be more complex since we need to structure the player path and puzzle for player to solve and it also increase the linearlity of the design.

So which in your opinion is the best design approach more memorable to implement to my game.

Thanks in advance...