Clearing Germany's migrant backlog
German Chancellor Angela Merkel has defended her policies on refugees, in the wake of recent terror attacks. As tensions grow, the government is still trying to deal with the large number of migrants who took advantage of Germany's open borders last year.
There were endless corridors where officials bustled through with files, offices with computers, microscopes and fingerprint-readers.
I saw signs for medical centres and canteens - some places freshly painted, others still being renovated.
Security staff were watchful, translators wrestled with all kinds of languages.
In individual rooms, intense conversations were under way between officials and families about life stories and dramatic journeys.
Anxious children looked up from parental laps, some playing with toys, others restless in stuffy waiting rooms.
Waiting is the key to this place.
For this is a new centre designed to end the long wait for hundreds of thousands of people who came to Germany last year as migrants - and who do not yet know whether they will be allowed to stay.
"Welcome culture" was the phrase used as Germany suddenly opened its borders.
Since then, the flow of migrants into Germany has hugely decreased as borders have closed and agreements such as the EU's deal with Turkey have kept many would-be migrants well away from Germany.
But the legacy of last year's mass arrivals is still very tricky for Germany - and even more so given recent violent incidents, some of which have been linked to recent migrants.
I was given special access to a new centre designed to show how Germany is responding to the crisis.
In the city of Bonn, it is a centre for processing asylum applications - one of more than 20 planned to deal with a huge backlog.
The numbers are staggering.
"We are pretty certain that by the end of the year everybody who came last year will have their application decided," I was told by Katrin Hirseland, from the Federal Ministry for Migration and Refugees (BAMF).
How many applications will have to be dealt with? "It will be somewhere between 800,000 and 1,000,000."
This presents a huge challenge for the government. How will it be done? In Bonn, the ministry has taken over the Ermekeilkaserne - once an army barracks.
It is a site full of history.
In the 1950s, when Bonn was the capital of the new West German state, the defence ministry was based here when the country was allowed an army again despite the horrors of Nazism.
Those horrors had persuaded Germany to create a generous law on political asylum for those fleeing persecution.
But it never imagined so many would come in such a short time.
Armin Moers, who runs this new centre, is a hugely energetic individual keen to show me how the system will work.
Up to 800 migrants a day could be brought here and their cases processed and decided in as little as 24 hours.
He showed me how migrants were registered and fingerprinted and their documents checked.
Many arrive without documents - either lost or deliberately destroyed, as asylum applicants know only those from certain countries will be accepted as genuine refugees.
In one room, I saw special equipment and computers used to detect forged documents.
One floor houses the crucial rooms where individual asylum hearings take place.
In one, I saw a Syrian family where the mother and son had just been removed so the asylum adjudicator could check the husband's story against that of his wife.
I listened as the adjudicator - a young, very focused woman - asked the husband about his journey from Syria, the details of where he had lived and how he had travelled.
Adjudicators all have access to a huge ministry database where they can cross-check stories as they decide whether applications are deserving.
The husband looked anxious, which is hardly surprising.
These hearings, which can take up to six hours, will determine the course of thousands of lives.
A computer network links what happens here to many other government agencies.
The aim, said Mr Moers, was to ensure that genuine asylum applicants could be helped swiftly to integrate into German society.
But about 40% of those applying for asylum in Germany are being turned down.
That means hundreds of thousands will be due for removal.
The idea of forced deportations is especially troubling given Germany's history.
Only about 22,000 were forcibly removed last year.
The government hopes to persuade many of those refused asylum to return voluntarily.
But some are already opting to disappear from official view, living underground, trying to avoid removal.
They can be vulnerable to economic and criminal exploitation, as well as radicalisation.
At the Bonn processing centre, I sensed a constant anxiety about security too.
Asylum applicants are not allowed to move around alone, and can leave the centre only with official permission.
And Mr Moers told me he did not want to give applicants a final verdict on their status here as he worried about a wave of anger threatening the security of his staff and other migrants - including children - at the centre.
Find out more
- Chris Bowlby presents Destination Europe: Germany - the Decision Makers on the BBC World Service from Thursday 28 July 2016
- Or listen via the BBC iPlayer
While the government acts, how has German society as whole responded to last year's influx?
I found a fascinating debate under way just a few yards away from the Bonn processing centre, in some buildings used by a local citizens' initiative.
They had been hoping to take over the empty barracks for community use, until the BAMF arrived.
Members have been helping migrants who arrived last year.
"It was amazing," Ute Harres, from the initiative, told me.
"It basically overwhelmed us."
Local people donated everything from clothes to bicycles.
And the initiative is still active, with projects such as cookery sessions bringing together children from local and migrant families.
At the same time, Ms Harres said, last year's arrivals had "brought up questions of immigration that have not really been tackled before".
Germany has had previous waves of migration - such as Turkish "guest workers" and refugees from former Yugoslavia.
But many of its people and politicians have always denied that Germany was "a country of immigration".
Now, said Ms Harres, people were debating how well integration was working, whether there were "parallel societies" in Germany.
People with reservations were "too quickly judged as extremists," she said.
"You need to be able to say, 'I'm right in the middle. I have reservations, but I'm also here to be open and welcome people.'"
So last year's "welcome culture" has not disappeared.
Many still want Germany to honour its generous recent tradition of asylum.
But there are worries too.
In a place like the Bonn processing centre, another priority is clear.
In increasingly insecure times, the government desperately wants to show it is getting a grip.