Terraria – How to stop monsters invading the mine/tunnels

There are several problems with hell and several ways to overcome them.

Hellstone

• Wearing an Obsidian skull will stop you being bunt from standing on it.
• Putting sand on top of the block before mining will remove the lava that is created.
• The buildings in hell give an excellent vantage point for mining the hellstone through the wall.

Lava

• Rocket boots allow you to cross large lava lakes easily, they are sold by the npc Goblin Tinkerer.
• Grappling hooks or Ivy whips work in similar ways.
• Placing sand above the lava will remove it when the sand falls into it, but you have to build up from the bottom.
• Water walking potions also allow you to walk on lava without being hurt.
• There is a trick with flippers that allow you to swim above the lava.

Baseline answer: A mob (evil NPC) must be standing on the same level as the door to open the door.

Mobs can jump but will generally only do a large jump if the player is near by. So while it may be possible for them to do so, it is not entirely likely. The thing I would be concerned about is when the monsters spawn on the ledges because you just happen to be standing at the right spot to make it a valid spawn location. Putting in good NPCs will help with this a bit, but its still a concern.

Here is a picture of my last base (well, two towers out of it, it expands more to the left with a couple more buildings). All the doors seen in the picture are mob safe, they are up one block from the standing level the mob will be on, and there is nothing for the mob to jump to as long as the door is closed. There is one weak spot on the right hand tower, if you look at the internal doors on the right side of it, they are on the level with the flooring.. So if a mob can get through the lower right hand door (which is offset properly mind you) then they can jump to to any level and start running havoc!

Hope this helps!