Player-made Structures

Caisson
A Caisson is a structure that allows characters to create shafts through water and empty space. It is simple to construct: simply place a row of blocks 4 wide underneath the character then mine out the center 2 blocks and repeat. If you wish to capture some water for the shaft you are creating, create a U shape out of blocks first and then continue normally.

Hellevator
Main Article: Hellevator

'Hellevator', also known as 'Hellvator', is the Terraria jargon for a drop from the main land to the underworld (Hell). It is a portmanteau of Hell and elevator, for obvious reasons. Usually at the bottom of a Hellevator is Water, since it removes fall damage, but you can also use Cobweb, Grappling Hooks, Ivy Whips, a Lucky Horseshoe or Rocket Boots.

House
Main Article: Home

A home is a safe haven for players or NPCs where they can spend their Nights without fear of attack under most conditions. If Blood Moon has risen, during which zombies can open doors, or a Goblin Invasion has begun, in which goblins can open doors, the home is no longer a guaranteed safe zone.

Defensive structures
Main Article: Home

Floating Base
Building your house in the air prevents any sort of land monster to enter your house regardless of their ability to knock down doors. Flying creatures can still be a problem but are easily nullified with platform traps and doors. Building a house like this is completely impregnable except by Goblin Sorceror, Worms or Bosses. As seen in the screenshot on the right, only one Zombie is allowed to spawn despite Blood Moon due to how many Demon Eyes are trapped, in addition the player can fight on the ground with melee or from the central "Airlock" of the house with ranged weapons. The only issue with this type of house is it can be detrimental to one's sense of reality.

Sand Shell Method
An effective Blood Moon/Goblin Night defense system includes sand on top of a torch, where the player breaks the torch and sand falls on the entire home, blocking off all entrances. A major drawback is that it is very tedious to clean up. You can make the sand as tall as necessary depending on how many entrances you have. However, setting up the system is comparitively tedious.

Tower Method of Self Defense
Utilizing a similiar method to the floating base however it is connected to the ground when it is locked down using two sand traps to block the bottom of the tower. The tower uses two platform traps to allow harvesting of Demon Eyes. The traps can be made into any prefered size. The advanced versions of the tower can use a secondary sand blocking system.