Walk out to Cromwell's Castle, Cromwellian in origin from 1653 and rebuilt as a gun position in the Napoleonic wars, still standing over the Shannon crossing

Find the Salt Battery — Fort Eliza — with its emplacements for four cannons, and the Martello tower

Walk the harbour and the marina on the Shannon

Find Charlotte's Way, the house once called Hill House, where Charlotte Brontë's widower lived out his life, and the house Trollope lodged in

Banagher sits on one of the very few crossings of the mid-Shannon, and it is fortified out of all proportion to its size. Cromwell's Castle, built in 1653, still stands controlling the river; so do the Salt Battery — Fort Eliza — with emplacements for four cannons, Fort Falkland, and a 19th-century Martello tower, all of them put there to hold one bridge. Anthony Trollope lived here in the 1840s, and Arthur Bell Nicholls came back to Banagher after the death of his wife Charlotte Brontë and lived at Hill House until 1906.

Banagher: The Shannon Crossing and Cromwell's Bridgehead

Clonmacnoise and the Shannon

Dublin

Ten nights in a loop from Dublin to the west and back: Clonmacnoise on the Shannon, three nights in Connemara for Roundstone, the Sky Road and Killary, then Croagh Patrick and Athlone.

Connemara and the West from Dublin

Walk the harbour and the lock where the canal drops into the Shannon

Find the ruins of the canal hotel that housed passengers overnight

Walk the Grand Canal towpath east from the harbour across the bog

Have a pint in one of the two pubs and watch the boats work the lock

Shannon Harbour is where the Grand Canal finally reaches the Shannon after crossing the bogs from Dublin, and for a century it was one of the busiest inland ports in Ireland — passengers and freight transferring between canal boats and river steamers, with a hotel to hold them overnight. The traffic went and the village stayed: a handful of houses, a lock, docking for boats, and two pubs. It is one of the quietest places on the whole waterway, and the junction survives largely as it was build canal junction in the country.

Shannon Harbour: Where the Grand Canal Meets the River

Stand under the restored Leviathan, the largest telescope on Earth in 1845

Find Mary Rosse's darkroom in the science museum

Cross the wrought-iron bridge of 1820, said to be the oldest in Ireland

Walk the walled gardens and find the 300-year-old box hedges

The 3rd Earl of Rosse built the great telescope at Birr, and when it was finished in 1845 it was the largest on Earth, able to see further into space than any before it. His son, the 4th Earl, measured the heat of the moon. After 1908 the telescope fell into disrepair, the mirror went to the Science Museum in London and the iron frame was melted down around 1914 for the war; it was restored in the late 1990s, and you can stand under it again. The castle is still the Earl's home, but the demesne is open: a science museum with Mary, Countess of Rosse's darkroom, thought to be the oldest surviving in the world, a wrought-iron bridge of 1820, said to be the oldest in Ireland, and box hedges more than 300 years old in the walled gardens.

Birr Castle: The Leviathan of Parsonstown

Find the Cross of the Scriptures and read the carved panels on it

Walk between the nine ruined churches and the two round towers

Look at the collection of over 700 early Christian graveslabs

Stand at the river and work out why the Esker Riada made this the crossroads of the country

Saint Ciarán, a Roscommon man from Rathcroghan, founded Clonmacnoise on the Shannon in 544 — and he chose the spot for a reason. This is where the Slighe Mhór, the great east–west land route, met the river after crossing the central bogs along the Esker Riada. Whoever held it controlled the crossroads of Ireland, which is why kings were buried here and why it was raided again and again. Nine ruined churches, two round towers, a castle and one of the greatest collections of carved crosses and cross-slabs in the country still stand on the riverbank.

Clonmacnoise: Where the Road Met the River

Walk the sculpture park and find the first pieces, made on the bog in 2002

Cycle or walk the trails across the cutaway bog

Find out what the Mesolithic camp found at Boora says about the first people here

Walk down to the angling lakes and the nature reserve

Boora Bog was cut away for peat by Bord na Móna, and the lake that gave it its name was drained. What was left has been given back: a nature reserve kept by the Irish Wildlife Trust, angling lakes, and Sculpture in the Parklands, a 50-acre land and environmental sculpture park that began in 2002, when seven Irish and international artists spent three weeks making the first pieces out on the bog. Excavations here also found a temporary camp from the Mesolithic.

Lough Boora: Sculpture on a Cutaway Bog

Go round Portumna Castle and walk the corridor that runs its whole length

Walk the Lough Derg shore in Portumna Forest Park

Watch the swing bridge over the Shannon open for boats

Find the old Famine workhouse on the edge of the town

Portumna, Port Omna, the landing place of the oak, is where the Shannon opens into Lough Derg, on the crossing between Galway and Tipperary. Portumna Castle was built in the early 17th century by Richard Burke, 4th Earl of Clanricarde, Lord President of Connacht — a semi-fortified house rather than a castle, with a three-metre corridor running its whole length — and was abandoned after a fire in 1826; its walled gardens survive. Beside it lies Portumna Forest Park. The bridge over the Shannon still swings open for boats, and the town's Famine workhouse stands on the edge of the town.

Portumna: The Earl's House on Lough Derg

Tour Athlone Castle, whose polygonal tower of 1210 is still the keep

Take a boat out onto Lough Ree from Athlone harbour at the lake's southern end

Walk Athlone's Left Bank, the old quarter between the castle and the river

Look up the lake to where Longford, Westmeath and Roscommon share its shores

Athlone grew up where the Shannon could be crossed, and that is why there is a castle here. The stone castle was built in 1210 for King John by his justiciar, John de Gray, bishop of Norwich, on a motte by the river, to hold the crossing and give the Normans a bridgehead into Connacht; it stands on or near the site of a wooden castle raised in 1129 by Tairrdelbach Ua Conchobair, and its polygonal tower of 1210, greatly altered, is still the keep. The town sits at the southern end of Lough Ree, the second-largest lake on the Shannon after Lough Derg, which forms the border between Longford and Westmeath on the east and Roscommon on the west. The old quarter, the Left Bank, is squeezed between the castle and the river.

Athlone and the Shannon's Lough Ree Shore

Find the octagonal lavabo, the washing house, the best surviving piece of the abbey

Walk the chapter house and trace the outline of the precinct

Stand where the Treaty of Mellifont was agreed with Hugh O'Neill in 1603

Work out what changed in Irish monasticism when the Cistercians arrived in 1142

An Mhainistir Mhór — the big monastery. Malachy, Archbishop of Armagh, founded Mellifont in 1142 to bring continental monasticism into Ireland, and it was the first Cistercian abbey in the country, and most of the others were founded from it. What survives is the octagonal lavabo where the monks washed before eating, the chapter house, and the outline of a very large precinct. It was dissolved in 1539 and turned into a fortified house — and in 1603 the Treaty of Mellifont, which ended the Nine Years' War, was signed in its grounds by Hugh O'Neill.