The three big cities of the British Isles share a language and little else: the currency changes, the balance between free and paid changes, and above all the time of year worth going changes. Below, what to know before booking.
London: the paradox of free
In London almost all the great national museums are free — the British Museum, the National Gallery, Tate Modern — and you pay only for temporary exhibitions. The cost sits elsewhere: £100-150 a day in mid-season, £150-220 between June and August and in December.
At the British Museum the donation asked for at the desk is voluntary, not a ticket. The busy window is 11am to 3pm: at opening the Rosetta Stone can be seen without a queue.
Two paid things worth understanding first. The Tower of London starts at £37 booked online and includes the Crown Jewels; Tower Bridge is a separate ticket and only buys the glass walkway. And on the Elizabeth Tower, Big Ben, UK residents go up free by asking their MP, while anyone from abroad pays £55 — 334 steps, no lift.
The free museum almost nobody knows is Sir John Soane's, the house-museum of a Georgian architect left exactly as it was in 1837 under the terms of his will: closed Monday and Tuesday, open Wednesday to Sunday.
Edinburgh: August doubles everything
Edinburgh costs £90-140 a day in mid-season, but in August — with the Fringe — and at the end of December for Hogmanay it climbs to £150-250. These are the city's two defining moments and also the two when finding a bed is hardest.
The rule that ruins the most days: castle tickets sell out online weeks ahead in summer, and once they are gone no more are sold at the desk. Online is cheaper too.
The rest is largely free: the National Museum of Scotland, with the roof terrace on level 7 that almost nobody finds; Arthur's Seat, 251 metres inside a park open twenty-four hours a day; and Dunbar's Close Garden, a formal garden hidden behind a gate on the Royal Mile, almost always empty even when the street above is packed.
The 1pm gun fires every day except Sundays, Good Friday and Christmas Day: half the city hears it and it costs nothing.
Dublin: the cheapest, and the most seasonal
Dublin is the best value of the three: €55-80 a day in low season, €80-120 in mid. The peak is March, with the St Patrick's Festival, when it reaches €120-180.
The verified gems are all away from the pub circuit: the Iveagh Gardens, the 'secret garden' hidden behind the National Concert Hall with its yew maze and waterfall, steps from St Stephen's Green and almost always empty; Marsh's Library from 1707, the oldest public library in Ireland, with its old anti-theft reading cages; and Drimnagh Castle, the only medieval castle with an intact moat in Ireland, 45 minutes from the centre by public transport.
When to go
For all three, March-May and September-October are the best compromise: manageable weather, shorter queues and prices far from the peak. Edinburgh in August is a conscious choice — either you come for the Fringe, and then book months ahead, or you avoid it. Dublin in March deserves the same reasoning around St Patrick's.