I'm looking into burrowing creatures that can leave a tunnel behind.
A creature with a burrow speed can tunnel through dirt, but not through rock unless the descriptive text says otherwise. Creatures cannot charge or run while burrowing. Most burrowing creatures do not leave behind tunnels other creatures can use (either because the material they tunnel through fills in behind them or because they do not actually dislocate any material when burrowing); see the individual creature descriptions for details.
So far I've found these that specifically state a tunnel is left behind:
What other burrowers from the Monster Manuals can leave a tunnel behind?
Preference for ones useable through high level [feat-enhanced] wild shape or shapechange