Koblenz is located within one hour travelling time of three major German airports:
Frankfurt, which is a main European hub and home of Lufthansa (rates will be comparably expensive),
Frankfurt-Hahn, which is a hub of the low-cost airline Ryanair and Wizz Air, Pegasus Airlines, Blue Air, & Iceland Express.
Cologne, which is served by major airlines and low-cost carriers as HLX, Germanwings, EasyJet.
Koblenz can easily be reached by train, for example from the Frankfurt/Mainz area, Cologne area or Trier. These towns are one to two hours trips and connections start early in the morning till late night.
Three German motorways lead to Koblenz: A3, A48 and A61. Parking in the center of Koblenz is restricted mostly to some hours. Park and ride is available. At train station is a park garage. Park garage at Löhr Center closes after shops closed and always some tourists forget this.
Many bus companies offer trips to Koblenz for one day ore more days.
At the train station is the bus central station. From there you can reach most areas of town (bus lines run mostly from 5:30 to 23:00). To "Festung Ehrenbreitstein" you go by bus or crossing the Rhine by ship and taking a cable cab up to it. From train station to the center it is only half an hour walk.
Deutsches Eck. This spot (the name means German Corner in German) is where the Mosel River meets the Rhein River. The tip of the park is shaped like a ship's prow, overlooked by an enormous equestrian statue of Kaiser Wilhelm mounted on an equally-huge stone base that you can climb for a great view of the rivers and opposite shore castle/fort.
Festung Ehrenbreitstein. This is a big military castle/fort in good condition. From there you have a good view over Koblenz (entry fee ca. 2 Euro). There is also one of the museum of Koblenz. It is located on the other side of the Rhine.
Militär Museum. This is a big military museum. It is located on the other side of the Mosel. In the past Koblenz was an important strategic military area. On every side of the rivers were military castles/forts. Rivers were the most important logistic routes till last century. Their possession decided win or lose of a war.
Schängler Brunnen. This is a nice little fountain near townhall. You should stand three steps in front of the fountain and in front of the figures face. Wait there three minutes. What then happens should bring fortune.
Watch Soccer at the Oberwerth-Stadium and see TuS Koblenz 
In August watch "Rhein in Flammen". At that weekend at the "Deutsches Eck" are concerts and on Sunday evening is a big fireworks. The history for this event is, that the Germans sent burning ships down the Rhine and confused the Roman troups. So they broke through the "limes", a wall, which protected the Romans from the uncivilized wild Germans.
In September is the "Nacht der Museen". On this night of museums special busses run among points of interests which are open till midnight. Ticket for entrance and bus is ca. 16 Euros.
Boating trips on the Rhine are famous. There are castles and vineyards to see.
Forty minutes by car or by train to the south is the famous "Loreley". In past that was a dangerous part of the Rhine for ships.
Koblenz has a classical theater. In Germany, men wear suits and women wear gowns when going to a classic theatre. In Blaue Biwel enjoy the cabarret. For young people there KuFa (cultur fabric) offers nice theater plays and concerts.
Koblenz has a big shopping mall(Löhr-Center) with some 130 shops, located in the city centre. There are also many downtown shops on or near Löhrstraße.
Excellent regional Wine and Food you'll find at Wirtshaus Alt Coblenz.
Koblenz is located among wine area of Rhine and Mosel. Most produced wines there are dry white wines. Dry red wines are available too. Vineyards are nice to look on Rhine and Mosel. "Königsbacher" is one local brewery of bier. Main difference between south and north German bier is the proportion of hops and malt. More hops makes beer more bitter. Using of more hops for beer is in this region common.
Irish Pub down the street away from the Deutches-Eck (german corner), is a friendly pub with english speaking bar staff, occasionally music.
The ****-Rhein-Hotel Diehl's Terrassen is situated directly at the Rhine, below the Ehrenbreitstein castle/fort, with a view of the Deutsches Eck from every room. Unfortunately, only a few metres from a busy railway. (Diehl's hotel)