What is the best mining tool? Terraria Guide:Mining techniques - The Official Terrarian Wiki
You can connect disconnected caves with shafts.If you can't go any further in the cave you're currently in, build shafts.
You might drown if you dig through water.The safest way to prevent this is to horizontally dig a tunnel of at least three tiles into the walls and then use the two tiles above the tunnel to create an air pocket.As torches won't work underwater, bring along some glowsticks, Flare Gun or Cursed/Ichor torches.
Blocks should be placed in the water where you want the walls of your tunnel when you come across water.Sand and Silt can be used.
You'll need to drain the water inside of the walls of your tunnel once it's completely sealed off.If there is a cave nearby, you can dig an outlet to let the water drain into it.You can start from the bottom of the tunnel.Blocks should be placed behind you before you dig through the water to prevent flooding.
If you have access to the Pumps, you can use them to move water from one place to another.You can place an inlet pump at the lowest point of your tunnel and wire it to an outlet pump.Attach a lever to the circuit to start draining water.
Solid blocks can't be placed in Lava, so digging through it can be a problem.You can use obsidian skin Potions to get fire resistance to dig through the lava and move it to a nearby cave.Bring a pickaxe that is capable of digging.Bring along some Gills Potions.Sand/Silt can be dropped into lava and replaced with sand.Bombs can explode through lava and can be used for small lava pits.
You can flood your tunnels with water if you don't have access to obsidian skin Potions.The walls of your tunnel will be formed from newly formed obsidian, and can be replaced with another block.As the tunnel is likely to be flooded, you may want to look for ways to breathe underwater, like the Gills Potion or digging an air pocket.
If you are doing this in the Underworld, you need to replace the water with Honey because it will quickly evaporate.
While exploring, traps can be found by using a Dangersense Potion, holding any wire related item, and looking for horizontal wire lines.Statues or geysers are possible if the lines are short and not straight.The geysers can only be found in the lava layer.
These methods can be used to find Dead Man's Chests, as the chest is connected with wires around the traps.
Managing the lava spawned when Hellstone is mined is one of the unique challenges of digging through the Underworld.
It makes mining Hellstone very easy because you are immune to lava damage.
You don't need to surround the Hellstone with blocks or move the lava to use obsidian skin Potions.You can easily access the Hellstone by jumping in one of the lava lakes.Most monsters will not be able to reach you.You can use a magic mirror to escape.
You can surround the Hellstone veins with blocks.When the Hellstone is mined, the lava will be contained.You can mine the Hellstone vein while standing outside.If you can't reach Hellstone, drain it or move it with pumps.
You can mine a small area under the Hellstone and suspend yourself above the spawned lava with a multi-latching hook.This technique requires precise control of your position and may make it difficult to reach veins in inconvenient locations, such as those close to a lava lake.