Underground Land Bridges Labyrinths

A fantasy setting where the major land masses are linked by a network of underground labyrinths could be fun to craft. Let try to generate one with 3 major land masses. 

First, let craft some quick random tables. 

Labyrinth's nature (d6) 

1. Natural network of caves. 
2. Crafted by giant ants or termites or other burrowing creatures. 
3. Crafted by an ancient human civilization using long forgotten magic or tech.
4. Crafted by an ancient near human civilization (dwarfs, trolls, elves, etc). 
5. Crafted by an ancient non human civilization (myconids, demons, neo otyugh, etc). 
6. Divine creation, crafted by an ancient divine entity.  

Paths (d6) 

1. Single path 
2. Single path, with two complications 
3. Two paths  
4. Two paths, one with two complications 
5. Two paths, both with two features
6. Three paths, one with two complications  

Path's Complications (d6) 

1. Partly flooded 
2. Very warm or cold
3. Infested by a swarm of creatures
4. Lair of a large and dangerous creature
5. Sealed a long time ago (locked doors that seal forgotten rooms and dangers) 
6. Trapped (natural or artificial hazards) 

Path's feature (d6) 

1. Precious mineral, fossils or gems veins
2. Concentration of magical resource 
3. Rich underground fauna or flora  
4. Wards against dangerous underdark creatures
5. Carved maps or sign posts 
6. Inhabitants (see table below)

Inhabitants (d6) 

1. Criminals, smugglers and bandits secret lairs  
2. Outcasts and refugees communities 
3. Guides safe houses 
4. Trade post or community of humans and underground species 
5. Guild houses (cartographers, geologists, prospectors, etc) 
6. Military outpost or Knight Order fort holding up against underdark creatures 
   

Now let establish 3 land masses and why their seas are hard to navigate. 

• Northern Lands (sea is often frozen) 
• Southern Lands (sea plagued by giant sea serpents) 
• Eastern Lands (frequent storms and tsunamis) 

The North-South Labyrinth 

• Crafted by an ancient human civilization who used forgotten geomantic magic.
• A single Path that is the lair of a large creature and that feature ancient magical wards.  

The North-East Labyrinth 

• Natural network of shimmering crystalline caves. 
• Path 1: Infested by a swarm or creatures attracted by a concentration of magical resources
• Path 2: Very cold and feature a community of underdark creatures and humans denizens. 
• Path 3: Trapped by magical radiations and precious fossils 

The South-East Labyrinth 

• Crafted by an ancient non human civilization of lava dwellers.
• Path 1: Partly flooded and lead to several pirates and corsairs hideouts 
• Path 2: Partly flooded, very hot, crossed by a magma river but also rich in gems