I think the last time I read a novel that had Horta tunneling through its pages was Dyson Sphere
, which I read last year on recommendation from this thread on hard scifi in TrekLit
. It was pretty good in the scifi department indeed, though somewhat clunky in the character department.
On the Horta front, it featured Starfleet ships with all-Horta crews filled with solid rock the Horta would reshape based on mission needs.