Skinny-dipping, gay relationships and parenting all form part of Magdi Gohary’s crash-course introduction to a strange new home, Learn to Understand Germany, given at a huge refugee camp on the outskirts of Munich.

Many of those who join his seminars headed to the country in search of security and gave little thought to what else awaited them there, says the 74-year-old, a retired chemist who left his native Egypt for Munich half a century ago.

“We talk about homosexuality, which a lot of my course members tend to see as criminal. I go on to explain to them that Germans don’t see it that way and that they will have to accept that if they want to live here,” he says.

They are warned that their children will have more independence if they grow up German than they might have expected in the Arab world.

“Arabs are often shocked here when they see the Bavarians go swimming naked in the River Isar. But I tell them that if they want the Germans to accept Arab women wearing headscarves then they must accept Germans sunbathing and swimming naked in public parks and rivers.”

In the wake of mass assaults on women in Cologne on New Year’s Eve – which police believe were largely carried out by men of Arab and North African backgrounds, including several asylum seekers – Germany is being pushed into a public debate about the challenges of integration.

The conversation is a delicate one. Refugees, those who work with them and the millions of Germans who support chancellor Angela Merkel’s policy of welcoming new arrivals are all very wary of giving more ammunition to far-right groups who have already made political capital from the attacks. But many are also frustrated by assumptions that it would take little more than a change of clothes and passports for new arrivals to settle in, and say the conversation is a very necessary one for Germans and refugees alike.

“Both Germans and refugees have expectations which the other side can’t really fulfill,” said Thomas Bönig, who runs intercultural city tours in Cologne. “There was a big hype two months ago, when it was seen to be cool and trendy to go to a refugee centre and donate old clothes, but this hysteria of joy is now turning into a hysteria of frustration. Just giving a refugee a donated jumper will not turn them into a German citizen. That needs time and both sides must approach each other with flexibility.”

Anas Alhamsho, a 36-year-old pharmacist from Damascus who has organised a petition condemning the attacks, readily admits that it has taken him time to adjust to his new home. “There is so much to learn about everyday life. Often it is little things such as respecting red traffic lights and not talking too loud in public. Just live by the rules like the Germans,” he says, more than a year after arriving.

Those challenges do not explain what happened in Cologne though, said Alhamsho, who has spent days travelling around refugee camps in the Ruhr valley to collect signatures for the open letter in English, Arabic and German that he hopes to deliver to Merkel this week.

“We abhor the sexual assaults and incidents of theft putatively perpetrated by migrants and refugees,” says the letter he drafted along with two other Syrians and a Pakistani. “We commit ourselves to do our part, within our means, to ensure that such crimes as were committed in Cologne will neither be repeated nor the hospitality of the Germans be abused.”

Refugees from Syria in Germany carry signs saying ‘Syrian refugees against sexual harassment’ to distance themselves from the New Year’s Eve attacks in Cologne. Photograph: Oliver Berg/EPA

There have been other spontaneous examples of public atonement, including campaigns to hand out leaflets and white roses with notes of apology, by refugees worried that the acts of a small group of men will be twisted to smear hundreds of thousands, and harden government policy on new arrivals.

“What happened was deplorable and unacceptable,” said Ghreeb Baccko, a 29-year-old Syrian who has recently arrived in the country. “I am afraid that these assaults could affect the way German society looks at migrants, especially as they could be used as an argument by opponents of the refugee welcome policy. Every day I read news about tightening residency measures.”

Many refugees are as keen as Merkel’s most hardline allies to see harsh penalties handed down to the attackers. Punishment of the perpetrators would protect both German women and the reputation of most refugees, they argue, at a time of steadily rising tensions.

Refugees have already been attacked by newly formed vigilante groups which have sprung up in recent weeks with names like Altstadt-Spaziergang (“Stroll through the Old Town”) and Block 4.

After Die Welt published the names and phone numbers of Alhamsho and the other coordinators of the letter, they received threatening phone calls. And in Bornheim, around 30km south of Cologne, the city government has banned all male refugees from using the swimming pools after reports of “verbal molestations”.

Germans who back Merkel’s policy and refugees themselves are fighting back, from lawyers tackling the swimming pool ban to others monitoring vigilantes. But with thousands of people still registering daily for asylum in a country only starting to explore difficult questions of integration, even some of Merkel’s supporters suggest Germany may struggle to cope if it does not halt or slow the pace of new arrivals.

Mr Hilmi, a 44-year-old engineer from Morocco who did not want to give his first name, has lived in Germany for decades. He volunteers to support refugees, but says the country cannot keep welcoming them at the rate of recent months. “Merkel’s ‘Willkommenskultur’ [welcoming culture] was right up to a point, but the government has long lost control. She should adjust her course to limit the inflow of migrants,” he said.

“The atmosphere has recently turned, especially here in Cologne.”

Already, he says, some Germans seem more afraid of people they think might be foreigners, and as a result he is making “small changes” to his life. He will be skipping the city’s carnival this year, normally a favourite celebration, because of worries about exposing his two young children to violence and racism.

“I would be concerned that the situation this year might be more tense than in the past. And I don’t want any trouble with drunk people who might say something offensive when they see someone foreign-looking.”

Gohary, the Egyptian who teaches cultural classes, worries that the Germans who welcomed them so enthusiastically also paid too little heed to the challenges of adapting to a very different country, while refugees expect more than an overwhelmed German state can provide. “Unrealistic expectations must be reconciled on both sides,” he says, but he sees hope in the fact that most refugees are eager to embrace their new home, and learn about even its most unexpected features.

“After the seminars the participants always come and ask when we could hold another such course,” said Gohary. “It is one of my goals now to recruit more people who could hold similar seminars because the curiosity of all these young refugees just shows what a huge need there is for that.”