Lots are accessible by train - like the fabulous Rhine Gorge and the fantastic Mosel Valley - two of the loveliest river valleys in Europe and a short train ride from Cologne - on the Rhine take a train to Rudesheim and hop on the K-d boats that do about a two-three hour trip north to Koblenz, going thru the finest part of the fabled Rhine Gorge - by the fabled Lorelei cliff and passing numerous wine towns and ruined castles and even one not ruined - Marksburg - boats go frequently enough so you can get off at one town or castle and then re-board the boat or there are also train lines along each side the Rhine in case you want to transfer from boat to train anytime.

For lots of great info on trains in Germany and this area in specific I always spotlight these IMo fantastic sites - www.bahn.de - the German Railways web site for schedules and fares and www.budgeteuropetravel.com; www.seat61.com and www.ricksteves.com.

Avail yourselves of bargain Lander Cards - unlimited rail travel in a wide regional area - two folks for 29 euros all day but you cannot ride the fastest trains but only regional trains - fine for a small area - buy these at stations once there.

For boat info www.k-d.com for the Rhine boats.

GREAT info - will definitely be put to use. Thanks! Mick

Aachen for the Aachener Dom (Charlemagne) and a very pretty Altstadt, and Monschau, a delightful small city situated in the gorgeous Eifel region.

The Lander Tickets mentioned by PalenQ are a great idea, but Cologne is notin the most "scenic" region to be able to take full advantage of that deal. Aachen, however, is within the region.

Other places within the Nordrhein Westfalen Lander region are Duesseldorf, with some fine museums, shopping and beer, and Munster.

I am sure your hosts will have a welath of other ideas for you, too.

Here is a Summary on the Lander tickets from the DB site, and the link;

>>Länder-Tickets
>>Days: Monday to Sunday
>>Validity: Unlimited travel for one day
>>Period of validity: From 9 a.m. (Mon-Fri) or midnight (Sat-Sun) until 3 a.m. of the following day
>>Area of validity: Throughout the relevant federal state
>>Trains: Valid for 2nd class travel on all regional trains, in many transport associations and on non-DB railway services
>>People: For 1 to 5 people
>>Fare: From 22 euros

http://tinyurl.com/bpzyvdw

I know a lot of people feel differently - but we much prefer to travel by car when we are heading into a bunch of small villages and countryside. If it were me, we would spend time with friends in Koln and see the sights immediately acessible by train.

Then we would probably rent a car for a week so that we could travel around the whole area without worrying about the location of train stations or schedules or have the frustration of seeing something that looks wonderful out of the train window as you pass by - and miss it.

Also, very highly reco visiting Aachen - it's a cute town - but has some wonderful historical monuments - and the chance to see something that was actually used by Charlemagne is just incredible.

(We also loved driving south from there through eastern Belgium and luxembourg - and seeing many of the small castles and military museums.

A very easy trip (by train, it is only a 15 minutes ride) can be done to Augustusburg castle in Bruhl.
http://www.germanplaces.com/germany/bruehl-castles.html

This is a historical building complex in Brühl,, which have been listed as a UNESCO cultural World Heritage Site, and it is the first significant creations of the Rococo in Germany.
The castle is famous for the magnificent staircase.

In Koeln you can see Ludwig museum (near train station and near the Cathedral}http://www.museenkoeln.de/museum-ludwig/default.asp?s=1808
It is a rich museum and it includes also some of Dali works.

"The Lander Tickets mentioned by PalenQ are a great idea, but Cologne is notin the most "scenic" region to be able to take full advantage of that deal."

The Middle Rhine Valley (the scenic region referred to by Aramis and Palenque) is indeed a unique and very worthwhile destination from Cologne:

http://www.welterbe-mittelrheintal.de/index.php?id=318&L=3

As Aramis says, you can't get there on a single "Länder Ticket" daypass since Cologne lies in a different "Land" or state. But if you arrange your trip on Saturday or Sunday, up to 5 people CAN get there and back on one daypass called the "Happy Weekend" ticket (42€) - OR, you can travel on a weekday for slightly more € with the "Quer durchs Land Ticket", another daypass option that permits travel across state lines (50€ for two.) These daypasses, like the Länder Tickets, offer impromptu travel on the regional trains and are described below:

http://www.bahn.com/i/view/USA/en/prices/germany/happy_weekend_ticket.shtml

http://www.bahn.com/i/view/USA/en/prices/germany/quer-durchs-land-ticket.shtml

Actually for anyone pondering using the train say on 6 or more days the German Twin Railpass can be a great deal if not confining yourself to one Land or small region and thus using Lander Tickets.

But a German Railpass can offer pricing at not much higher per day than even the Lander tickets and you can hop on any train anytime - full flexibility - Lander tickets restrict you to slow stopping regional trains - so check out the German Twin Pass for complete flexibility to hop any train anytime and expand your horizons from the immediate Cologne area - in a few hours you could be in Heidelburg, Marburg, Trier, Cochem on the beautiful Mosel, Baden-Baden, Freibourg, etc.

A 6-day German Railpass (Twin) two names on one pass - p.p. costs about 28 euros a day for fully unlimited hop on any train anytime travel - great for traveling between Landers and even for use inside Landers if you want to take the fastest and most comfortable trains.

28 euros a day for fully flexible travel - can save tons on longer trips and not have to lock yourself into some non-changeable non-refundable ticket. Hop on any train anytime for 28 euros a day - and if you want more days - say a 7-day pass the extra day is only $21 a day or 15 euros a day - 15 euros a day is about as cheap as the 29 euro Lander Card for two people and there are no restrictions.

You might like to visit Maastricht in the south-eastern Netherlands - a pretty little city and a bit different to the German architecture. I also second Aachen, lots of history there.

Lavandula

Congratulations! What a wonderful opportunity you have.
In Koln itself, in addition to the usual tourist sites, I suggest the following:
- The El-DE Haus, Nazism Documentation Centre in a former Gestapo HQs, if you’re the least bit interested in the Cold War
- Kölnisches Stadtmuseum, one of the largest, most diverse and interesting city museums I’ve seen
- Roman-Germanic Museum – I loved it and this period of history is far from my favorite
- The 12 Romanesque Churches
- Stoplersteine (stumple stones) scattered through town and the old wall

I second the recommendations to visit Aachen, Maastricht and Augustusburg. Don’t miss a tour of the Rathaus in Aachen. I’ve never been to Düsseldorf, but if you’re a beer drinker, I’m told it’s worth a visit.

I also agree with nytraveler that having a car is often helpful when visiting the smaller towns. Cars are not helpful in larger towns/cities where you drive to your location, park the car for the day and then drive back to your origin. In your case, if you decide to rent a car, be sure you make the most of it. Does your host have a place to park it, or will you have to find a place and pay? If you’re paying for parking every day, it may not be worth it. Or, plan a few days of travel away from your host city and see those things less accessible by train.

Some additional suggestions:
- Münster – an interesting town full of sculptures, the heart of the Anabaptist revolution, and see where the Treaty of Westphalia was signed
- Essen – European Capital of Culture in 2010, once a gritty mining town, it’s interesting to see how it has transformed and how the old mines have been repurposed
- Koblenz – where the Rhine and Mosel meet. See the Deutsches Eck, Ehrenbreitstein Fortress, and enjoy the quaint town and good wine. Could be combined with a K-D cruise on the Rhine.
- For a taste of edgy Belgium, consider Antwerp
- For a taste of Luxembourg, consider the lovely town and castle in Vianden

Bonn is a quarter of an hour away. You can find some very interesting museums there (building some of them had just started when it was decided to move the capital to Berlin).

ttt