Ermine Street was the Saxon name given to the Roman road linking York with London. Of course, pilgrims will also have come from further N than York: from Scotland, Newcastle and other towns, or from shrines such as Lindisfarne or Durham. But many of these will have gone by sea rather than overland to the S coast. So, because York was the major town of the N of England, this page starts there.
Besides the Minster of secular canons, the largest of all church buildings in Britain, York also had many monastic buildings. Remains can be seen of 2 Benedictine foundations: St Mary's abbey, which was the largest in the N of England; and Holy Trinity priory, Micklegate. Nothing remains of the 2 other Benedictine houses, the Gilbertine priory, or any of the friaries. (See The Orb site for map and info on the friaries.) A C15 window in the N Transept of the Minster depicts the life of St William; the C14 Pilgrimage Window in the N nave aisle shows pilgrims at the shrine - see York University's Medieval Yearbook for a discussion of symbolism in this window.
From York, Ermine St headed SE and crossed the Humber at Brough. The only crossing now is the Humber bridge, the route is largely main road, and in any case pilgrims may well have made a detour to the shrine of St John at Beverley. A possible route there, though somewhat meandering, is the Minster Way. Just E of York, St James in Murton was a chapel of ease for Osbaldwick, now a suburb of York. Near Pocklington, Nunburnholme has a church of St James with a Saxon cross inside. Nearby, nothing much remains of the Augustinian priory at Warter; the church of St James is C19. The Dominican friary in Beverley is now the Youth Hostel, so can still be used for accommodation. W of Beverley is Walkington, where the High Hunsley Circuit, then the Wolds Way can be taken to the Humber bridge.
On the Lincs side of this, Barton-upon-Humber has a fine Saxon/Norman church. To the E, Barrow was the site of a Saxon nunnery, and SE of this, at Thornton, the impressive gatehouse and chapterhouse remain of the Augustinian abbey.
SW of Barton too were some small priories: at Bonby there was an alien one, of which nothing remains, and the only trace of the former Augustinian one at Elsham is a fishpond. On the W side of the river Ancholme, either side of Ermine St S of Appleby, a derelict farm is probably on the site of the small Cistercian nunnery of Gokewell, and the Explorer map marks the scanty remains of Augustinian Thornholme.
The riverpath can take you S from Brigg, past Newstead Priory where a Norman vaulted room and a window are what remains of the former Gilbertine foundation, and Winghale Priory, where the building of that name is the descendant of a small alien Benedictine cell of Sées.
W of Ermine St, at Willoughton, are the sites of both a Templar, later Hospitaller, preceptory (the wealthiest in the country) and a small Benedictine priory. SE, at Spital-on-the-Street, the chapel-of-ease of St Edmund is what's left of a medieval Hospital, which served pilgrims.
At Lincoln, the Minster, like York and Beverley, was run by secular canons; it housed the shrine to the Carthusian St Hugh. Greyfriars, the former Franciscan friary, is seeking alternative use. There are also remains of the Benedictine priory, marked Monk's Abbey on OS maps, which was dedicated to Mary Magdalene.
From Lincoln, Ermine St heads S and for once is not a main road; the Viking Way follows or shadows it for a considerable distance. From W of Sleaford, however, it is major road all the way to London. So, just after Temple Bruer, where, to the E of the Street, the tower at Temple Farm is what's left of what was one of the largest Templar, later Hospitaller, preceptories, head for Rauceby (where there used to be a church of St James, long vanished) and Sleaford, where there was a bishop's palace, and where another Roman road, Mareham Lane, can be followed/shadowed S. S of Threekingham, OS maps mark the site of the former Priory of Sempringham, where Gilbert founded the Gilbertine Order, the only English monastic order. Little remains except a few mounds, some fishponds, a holy well, and the church, now dedicated to St Andrew. To the NE, at Bridge End, Priory Farm marks the site of a further Gilbertine priory.
To the SW is Aslackby, where the church, dedicated to St James, has a E window with a scallop-shell flanked by the crosses of the Knights Templar and the Knights of St John, who formerly owned this site; the Explorer map marks Temple Farm. From here, continue on to Bourne, where the Augustinian abbey now serves as the parish church. A path leads S along Car Dyke, a Roman waterway from Peterborough to Lincoln, to Baston; continue to Deeping St James, perhaps along King St, yet another Roman road, and the river path. The fine church of Deeping St James remains from the Benedictine priory, though the St James window is C19.
Next stop is Peterborough, but there are 2 other abbey, now parish, churches nearby that might be worth a detour: Crowland, further down the river Welland, with its cult of St Guthlac; and Thorney, cult of St Botolph. There are however not many footpaths in these parts.
Like any other self-respecting abbey, Peterborough had a cult, of St Oswald, but this appears not to have been very important. The large church of the Benedictine abbey was however very important and is, of course, now the cathedral.
From Peterborough, Ermine St heads S to Godmanchester/Huntingdon. As an alternative to the main road, head for Ramsey, where a school incorporates most of the remains of the Benedictine abbey, though the gatehouse belongs to the National Trust. S of Ramsey, the medieval church of St James in Little Raveley is now a private house.
SW of Huntingdon is Hinchingbrooke House, where a few stones are all that remains of the Benedictine nunnery of St James-extra-Huntingdon. The nunnery is still remembered in the name "Nuns' Bridge", but the more impressive bridge, built by the monks of Ramsey with its own chapel in the middle, is at nearby St Ives. To the W of the bridge is Hemingford Grey, where the church is dedicated to St James. E of St Ives, the village of Needingworth formerly had a chapel of ease dedicated to St James, and the village of Holywell still has its eponymous holy well in the churchyard.
From Godmanchester, you can shadow Ermine St by taking the Pathfinder walk S to Yelling. S of here, Croxton has a St James church, as does Waresley further S again, though see here for details of its complicated history. From here, tracks and paths, partly on the Clopton Way, can take you to Royston, where you cross the Icknield Way. Then the Hertfordshire and Harcamlow Ways can take you S, shadowing Ermine St to Ware, where the council has converted the remains of the Franciscan friary for use as offices. From here, you can use the Lea Valley Walk to Waltham Abbey and London. S of Ware, near where the Stort flows into the Lee, Stanstead Abbotts also has a church of St James, now Churches Conservation Trust.
It's entirely possible, though, that pilgrims followed the river valleys via St Albans from Huntingdon to Waltham. A modern route largely uses waymarked long-distance paths. First take the Ouse Valley Way S. This passes Little Paxton, where the church of St James has a Romanesque tympanum. St Neots, named after a Cornish saint, had a Benedictine priory, though nothing remains of it. Leave the Ouse valley via the Ivel, continuing to Blunham, where John Donne was rector of the church dedicated, unusually, to St Edmund, King and Martyr, and St James. The riverside path peters out at Sandy, so take the Greensand Ridge Walk to Warden - where nothing much remains of the Cistercian abbey apart from a vineyard of that name - and Chicksands Priory, where the cloisters remain of the Gilbertine foundation. The John Bunyan Trail heads S to Icknield Way.
Continue on the Chiltern Way extension round the E edge of Luton (and the airport) as far as Redbourn; then the Hertfordshire Way which shadows Watling St into St Albans. This was an important pilgrimage centre of the first known British martyr, where the large Benedictine abbey is now the cathedral.
From here, the obvious route into London is Watling Street but, despite the presence of (largely Victorian) churches of St James off-route at Bushey and Friern Barnet, this is not very scenic, so an alternative is to head for Waltham Abbey and approach London via the Lee Valley. You can reach Waltham either via the cycle-path to Hatfield, where a palace of the bishop of Ely was converted to a royal palace and is now Hatfield House, and then the Lea Valley Walk to Ware and Waltham, or more directly using the Hertfordshire Way and Chain Walk between S Mimms and Waltham Cross.
Waltham Abbey was the largest Augustinian church in England, and the nave of the church remains, as do some other remnants of this formerly important shrine of the Holy Cross. Little, however, remains of the Benedictine nunnery at Cheshunt on the other side of the river.