Option 1: You can give the token sight and give them control of the token, then lock the token. That way they cannot move the token, and you simply need to unlock the token when you want to move it yourself. Option 2: Create a token and give it sight and give your players control of it. Create a transparent image that is the size of the entire map that your players have control over, put it on the Token layer, and move it 'to front' (in front of the 'sight' token) and lock it. Your players will not be able to select the 'sight token'. Option 3: Take the master map image of the dungeon into a photo editing program and splice out each area into separate images. Put the spliced images into place on the GM layer, and as your players move through them, flip the area to the Map layer. Option 4: Use Permanent Darkness/Fog of War to cover areas with a black overlay that your players can't see through, and reveal those areas as they move through. If you are not using Advanced Fog of War or Updated Dynamic Lighting, then you don't need a 'sight' token at all. You can put a 'You are Here' token that they can't control on the Token or Map layer.
