There are also some fragments of (probably late medieval) glass in the lights of another window, including this heraldry, crossed keys surmounted by a crown, within a wreath.
But it's the sculpture in the church that most sticks in the mind.
In the chancel is this monument to Sir John Halsey, who died in 1670. It's attributed to John Bushnell (c.1630-1701), part of whose story I related when writing about the monuments in Little Gaddesden. It's an unusual design, highly baroque; essentially it's a mantlepiece-like shelf supporting a seemingly precariously balanced bust of Sir John (who twists his head to one side). There are flanking urns. The shelf is supported by two putti heads and a large cartouche (which is in turn supported by a smaller cartouche), full of strange, swirling almost hallucinogenic shapes that always seem to be on the verge of morphing grotesquely into something else. At the top there's a more or less recognisably human head, but the heraldic shield below is grasped by two maggoty monsters and, at the very bottom a moustachioed face has, where you'd expect to find eyes, another, bigger nose. It's almost tempting to see in this Bushnell's personal eccentricity, which sadly ended in insanity.**
In the Shell Guide: Hertfordshire R M Healey, who can usually be relied upon to have catholic tastes and find value in work of all periods, describes the monument as 'Probably the ugliest in Herts, a waste of marble.' On the other hand Pevsner calls it an 'exceptionally good Italian-looking monument with finely designed cartouche and, on top, a Berniniesque bust'.
Great Gaddesden is a good place for spotting spotted Hertfordshire puddingstone, a 'silica-cemented conglomerate composed of flint pebbles and cobbles with [a] matrix of fine sand and silica cement' (Wikipedia). Alec Clifton-Taylor (in the chapter on geology in Bettley/Pevsner) calls it 'a kind of natural concrete' and remarks that 'although [it is] much tougher than the ginger-coloured puddingstone of Essex, it is a material which nobody would think of using for building unless there was nothing better; but in Hertfordshire this was sometimes the case.' As indeed it was in Great Gaddesden; lumps of it can be seen at the base of several buttresses, for example, and the ungainly chunk pictured above is lying around in the churchyard.
* The otherwise quite useful church website states that "As you enter from the porch you step down into the church; this is often a feature of churches dedicated to St John the Baptist, as Jesus stepped down into the River Jordan to be baptised." This is another romantic story, along with weeping chancels, Devil's doors and cross-legged Crusaders, for which there is absolutely no contemporary evidence and that has been thoroughly debunked and yet lingers in the popular imagination. It's true that some, probably many, churches dedicated to John the Baptist have steps leading down into them. But it's also true that many churches with other dedications have the same feature, because the ground tends to rise over the centuries. To imagine there's any symbolic meaning behind this is mere wishful thinking. Widford is another Herts church making this claim. Hinxworth church has no fewer than five steps down into the nave. It's dedicated to St Nicholas.
** There's another somewhat similar grotesque head of about the same date in the county in the 1687 Goulston monument in Wyddial.
*** Margaret Whinney, Sculpture in Britain 1530-1830, Harmondsworth, 1988.