1 Of that same wood it framed was cunningly,
framed > fashioned, made cunningly > skilfully; with occult knowledge
2 Of which Caduceus whilom was made,
whilom > in ancient times (see Aen. 4.242-6)
3 Caduceus the rod of Mercury,
rod > wand Mercury > (Representing, and often synonymous with, Hermes, the envoy of the gods; employed by them to conduct the souls of the dead from the upper into the lower world. According to Virgil, his wand also allows him to summon these souls back from hell. Mercury is identified as the god of reason and wisdom)
4 With which he wonts the Stygian realms invade,
wonts > is accustomed to Stygian > {Of the River Styx, one of the five rivers of hell; hence: infernal} invade > enter (SUS); hence: explore
5 Through ghastly horror, and eternal shade;
ghastly > {Evoking fear of the supernatural}