Built as the mausoleum of the emperor Hadrian, converted into a fortress when Rome’s walls needed strengthening, then taken over by the popes as a stronghold and refuge, connected to the Vatican by a walled passage, used as a prison, and now a museum.

That sequence is legible as you walk. You climb through the Roman core, past medieval fortifications, into Renaissance papal apartments, and out onto a terrace.

The cylindrical shape and the enormous scale are the Roman tomb underneath everything else.

The bronze angel on top commemorates a vision of the archangel Michael sheathing his sword, which gave the building its name.

It sits on the river directly opposite the bridge that leads to it, a ten-minute walk from St Peter’s Square.

The single best thing here and the reason most visitors rate it so highly.

The terrace at the top runs around the building and gives a full panorama: St Peter’s dome directly ahead across the rooftops, the river bending below, the historic centre laid out on the other side, and the hills beyond.

The view of St Peter’s from here is better than any view available from St Peter’s itself, and it is the shot people take home.

There is a café on the terrace level, which makes it possible to sit with the view rather than photograph it and move on.

Go late in the day if you can. The dome catching the last light with the city in shadow below is the version worth waiting for.

The way up is part of the visit rather than a means to it.

A Roman spiral ramp climbs through the centre of the building from the base, the original processional route into Hadrian’s tomb, still with sections of ancient paving and the marks of two thousand years of use.

From there the route continues through the fortress levels, the papal apartments with their frescoed rooms, the armoury and the prison cells, and finally out onto the terrace.

It is a continuous climb with steps and slopes and no lift on the standard route.

That climb is the thing to be aware of when planning. It is not difficult for most people, but it is sustained and there is no shortcut to the terrace.

The elevated walled passage running from the castle to the Vatican, built so that a pope under threat could escape from the Apostolic Palace to the fortress.

It was used in earnest more than once, most famously during the sack of Rome in the sixteenth century.

You can see it clearly from outside the castle, running along the top of a wall toward the Vatican, and sections are open to visitors at certain times or on specific tours.

Access varies by season and by ticket, so check what is currently open rather than assuming.

Even from the outside it is worth knowing about — it explains why the castle exists in the form it does.

Tickets are sold online and at the door. Queues are usually modest by Roman standards, and this is one of the few major sites where turning up works reasonably well.

Booking ahead is still sensible in high season and saves standing in the sun.

Roma passes and combined tickets often include it, which is worth checking before paying separately.

Special evening openings run in the warmer months, with the terrace open after dark and sometimes with music or events — these are the best version of a visit here and need checking against your dates.

Prices change periodically, so check the official site rather than any figure quoted elsewhere.

The pedestrian bridge leading to the castle is an attraction in its own right and costs nothing.

It carries ten angel statues designed by Bernini, each holding an instrument of the Passion, lining both parapets.

The view from the middle of the bridge — the castle ahead, the river below, St Peter’s dome to the left — is one of the classic Rome compositions and is best at sunset and after dark when everything is lit.

Street sellers work the bridge, and it gets busy in the evening.

Cross it slowly rather than treating it as the approach to the ticket office.

Ninety minutes to two hours for the full route including the terrace and the papal apartments.

An hour if you are heading straight for the view.

Add twenty minutes for the bridge and the exterior, which are free.

It pairs naturally with the Vatican, ten minutes away on foot, and is a good afternoon counterpart to a morning in the museums — considerably calmer, with a view of the dome you have just been standing under.

It also works well as an evening visit when the special openings are running.

Late afternoon into evening is the best of it, for the light on the dome from the terrace.

Early is quietest and is a good option in summer heat.

The middle of the day is busiest and the terrace is fully exposed to sun.

Evening openings in the warmer months are the standout — the terrace after dark with the city lit is a different experience from the daytime visit, and far fewer people take it.

Check closing times, which vary by season, and note that the last admission is well before closing.

October and September are the busiest months, with March, April and May close behind — a flatter distribution than most Rome sites because a good part of the visit is indoors.

January and December are the quietest.

The terrace is exposed, so a clear day matters more here than at an indoor museum.

Winter gives sharper air and better long views, with far fewer people on the terrace.

Summer evening openings are the reason to come in the hot months rather than the middle of a July afternoon.

There is a café on the upper level with terrace seating and a view, which is the best-placed café at any Roman monument.

Toilets are available.

There is a shop.

Seating exists at several points on the route, which matters given the climb.

Carry water in summer; the interior is stone and cool in places but the terrace is fully exposed.

Limited on the standard route. The building is a Roman tomb converted repeatedly, and the climb involves ramps, steps and narrow passages.

There is a lift serving part of the route, which improves access to some levels — check what is currently operating with the museum before relying on it, since coverage does not extend to everything.

Reduced or free admission generally applies to visitors with disabilities and a companion.

The bridge and the exterior are level and free, and the view of the castle from the bridge is a substantial experience in itself for anyone unable to climb.

The riverside walk alongside is level.

This is one of the best-reviewed sites in Rome and the criticism is thin — mostly that the interior interpretation is patchy and that some visitors expected more furnished rooms.

The thin version: climb quickly, take a photograph from the terrace, come down, and treat it as a viewpoint with an entrance fee.

The good version: cross the bridge slowly past the Bernini angels, climb the Roman ramp knowing it was built for Hadrian’s funeral procession, walk the papal apartments and the prison cells, come out onto the terrace in the late afternoon with St Peter’s dome in front of you, and have a drink at the café while the light goes.

It is quieter than the Vatican, cheaper than most Roman sites, and it holds two thousand years of the city in one climb.