A birthday boy guarantees Hamburg survival, bomb-blast victim Marc Bartra sheds tears on his Dortmund return and RB Leipzig are on the end of another unsavoury incident.

Here are five things we learned from the final round of Bundesliga matches this weekend:

Cologne return to Europe

Cologne ended their 25-year wait to play in Europe by finishing fifth thanks to their 2-0 home win over Mainz, helped by Hertha Berlin's 6-2 thrashing by Leverkusen.

Germany defender Jonas Hector and Japan striker Yuya Osako scored the goals to give Cologne a Europa League place next season.

It is the first time they have qualified for Europe since being knocked out of the UEFA Cup first round in 1992/93.

"What has happened here in the last few years is like a fairytale," said goalkeeper Timo Horn.

Austrian coach Peter Stoeger is credited with the revival in Cologne's fortunes, which started when he steered them to promotion from the second division in 2013/14.

His players sneaked into the post-match press conference to pour beer over him in mid-sentence, leaving him to joke: "Five players will have to look for a new employer."

Hamburg know how to survive

Striker Luca Waldschmidt scored on 88 minutes, 110 seconds after coming off the bench, to seal Hamburg's dramatic 2-1 win over Wolfsburg to lift them out of the relegation places.

"That was the best moment of my whole career," said Waldschmidt, who turned 21 on Friday,

His first Bundesliga goal prompted wild celebrations as Hamburg escaped relegation for the fourth time in six seasons.

"I have no idea how it went in -- I'm not usually the best headerer of the ball," he added.

Hamburg's first win in six games left them 14th and pushed Wolfsburg, the 2009 champions, down to 16th to face a two-legged relegation play-off to stay up.

Freiburg will cheer Dortmund

Freiburg's players, staff and supporters will be Borussia Dortmund fans for one match only in Saturday's German Cup final in Berlin.

Freiburg, last season's second-division champions, lost 4-1 at Bayern Munich on Saturday, dropping to seventh in the table -- just missing out on a Europa League place.

But if Dortmund beat Frankfurt in Berlin, their Europa League place as German Cup winners will go to Freiburg because Dortmund have already qualified for the Champions League.

"I'll cross my fingers from the bottom of my heart for Dortmund and hope that thanks to them we get a chance to play in Europe," said Freiburg's Nils Petersen, who scored a league-record 19th goal off the bench in Munich.

Bartra's emotional return

Marc Bartra shed tears after Dortmund's 4-3 win over Werder Bremen as he played his first game since fracturing his wrist in the April 11 attack on Borussia's team bus.

"This is one of the most beautiful days of my career. My family is here, there are so many emotions," said the Spaniard, who cried openly while celebrating with team-mates.

The centre-back had shards of glass surgically removed from his wrist after three bombs hit the Dortmund team bus on the way to last month's Champions League quarter-final home to Monaco.

Dart attack on RB

RB Leipzig, backed by energy drinks giants Red Bull, got another reminder during their 2-2 draw at Frankfurt that the commercialism they are seen to represent means they are not Germany's most popular team.

A dart hurled from a block of Frankfurt supporters just missed a group of Leipzig players celebrating Marcel Sabitzer's opening goal after 25 minutes.

"Thankfully it had a plastic -- not a metal -- tip," fumed Frankfurt chairman Axel Hellmann.

"Quite clearly, that sort of thing has no place in football."

This is the latest incident to target second-placed Leipzig this season.

A severed bull's head was thrown onto the playing area in Dresden, a fan protest delayed the RB bus in Cologne and Leipzig fans, including women and children, were attacked by fans in Dortmund.