If sightseeing is what you are after: Official Cologne-tips are to be found on the city's website. A list of activities can be found on Tripadvisor.
More christmas and wintermarkets can be found here. We recommend the hipp-alterantive Market at Stadtgarten (very close to DaHeim V56) or the wintermarket at media market - if it is something
different you are after. If you like it more traditional: the markes at Cologne Cathedal might be the most expensive, but also oozes atmosphere as the one at Alter Markt and Heumarkt (the
latter has a very popular ice rink). This one remains open after christmas and is called winter market. There are also very small but nice christmas markets in Ehrenfeld (if you want feel more
like a local) at the Herbrands - providing mainly local producers the
opportunity to sell. Also at Buhmanns there is
a very small market that attracts the hipper crowd.
Activity wise we can recommend the chocolate museum (if you are into chocolate), of course visiting (and possibly also climbing) the cathedral.
The tourist information is in your back when you stand in front of the main entrance of the cathedral. So if you want to pick up a map or get some additional suggestions, that would be the place (They also sell quite funky Cologne inspired gifts in the basement, if you are on the lookout for that).
One of our favourite churches in town is a small one called St. Ursula - a mere 5-6 minutes walk from the cathedral where you learn about the towns patrons myth: Ursula defended the city with her 11.000 virgins against the Huns and thus became the citys patron. Every day there are timeslots where you can also see the gold chamber decorated with real bones, supposedly from the virgins and lots of relicts. Good fun: ask to shake the skull with the bones inside for good luck. Also there is a big replica boat in the main church and you can see her grave. Ask at the tourist information for opening hours. Church to be found here: Ursulaplatz 24, 50668 Cologne.
What is more: museum wise we can whole heartedly recommend Columba Museum. It is a catholic museum but spectacular. It only opened a few years ago using an old bombed church from WW2 as part of the exhibition space.
Then of course there is always also the modern art museum (Ludwig Museum) as well as the medieval art museum (Wallraff Richartz Museum) to keep you happy too...
A fantastic recently newly built museum is the anthropological Museum - the Rautenstrauch-Joist Museum. Again you will find an astonishing architecture which is just as exciting as the exhibits. Guided tours are highly recommended!
The house in Glockengasse number 4711 is the birthplace of the perfume brand 4711. There is a perfume fountain and on the hour you can see and hear a beautiful merry-go-round in the tower of the house (listen closely if you can recognize some of the melodies - which are all to do with the history of the house and the city of Cologne).
Definitely do not miss out on sampling some Koelsch, the local beer tradition in one of the many breweries in the old town. The old town is in itself a nice place to explore with lots of old buildings, munuments, museums and the town hall. Get yourself some yummy icecream in the old square (Alter Markt) and have a look at the statue of Jan & Griet in the middle of it.
Do note: (probably) nowhere else in the world is drinking alcohol on the street so accepted as in Cologne. The „Wegebier“ (literal translation: a beer for the way/ literally to go) is the typical accessoire of old and young, for normal people as well as hipsters. It is being bought from the next kiosk (they call it "Buedchen" in Cologne). Thus people walk with it throughout the city, as if it was their newest handbag or lover. Like in Italy and Spain squares are taken by swarms of people caring their own bottles (such as the Brussels Square in the Belgium Quarter).
Does that sound too boring? If you want to get to know Cologne from a different side you should try one of the following:
A tour of a very special nature is the one you can do over the Roof of the Cologne Cathedral. Do not mistaken this for the climbing of the south tour of the cathedral which is open to anyone who is crazy enough to drag him or herself up those stairs ;) The tour takes you up in an
elevator. You will need to book the tour at least 6 months ahead as it is sought after and you should be a group of people (max: 17 persons). It really is a special way of getting to know the
cathedral and its surroundings. Really beautiful views can be had from up there. Recommended!
A new adventure is Time Ride. With 3-D
glasses on you can experience life as it was in the time of the Kaiser (the big Emperors in the 19th century). Lots of fun. online booking recommended.
Who does not want to listen to tourguides merely telling stories, they can interact by solving a murder mystery tour by Citythriller. In small teams you will become the investigators, who trace suspects and interrogate real live players to try to gain insights into who did it. This really is good fun!