The best way to arrive in Llangollen is by car. The A5 (from London to Holyhead) runs through the town. There is also a bus service from Oswestry, about 15 miles away.
Llangollen is a small town and all the tourist attractions can be reached on foot. The town centre basically consists of one main street running between the A5 and A539, most of the other roads lead off this. There is cheap car-parking in the town-centre, just off the main street.
As you approach the town you'll see the Pontcysyllte aqueduct carrying the Ellesmere Canal over the River Dee, its over a 100 feet high and a 1000 long. The aqueduct is quite an impressive sight, especially when you consider that it was built over 200 years ago.
There is a ruined castle, Dinas Bran, just outside the town. There is no admission charge but the view is worth the long walk/climb.
Visit Plas Newydd a half-timbered black and white house in its own grounds. The inside has been intricately carved and looks surreal to say the least!
Every year Llangollen hosts an International Eisteddfod where people from all over the world take part in musical and dancing competitions. 
The Llangollen Steam Railway departs from the station in the town. You can enjoy a 3-course meal on the train or just go for the ride.
Horse-drawn canal boats are available 50 meters from the town center at weekends and during the summer. Make sure you sit on the right side of the boat and then you'll be able to look over the side and down a 100ft drop as you pass over the Pontcysyllte aqueduct!
The fast flowing and rocky River Dee is popular with canoeists. You'll have to bring your own canoe though.
The town has the usual selection of gift shops that you'd expect to find in Wales. There is/was an antiques centre.
There are a wide selection of hotels and restaurants, including Indian,Italian and Chinese.
According to a recent TV programme Pavarotti was so impressed by the food at the Chain Bridge Hotel, when he stayed there during an Eisteddfod, that he later asked for some local delicacies to be sent to him in Italy.
Most of the pubs are worth a visit. The Bridge End Hotel is popular with bikers and often hosts rock discos at weekends.
There are a number of cheap Bed & Breakfasts in the town.
The Wynnstay, Smithfield and Bridge End Hotels also offer cheap Bed & Breakfast accommodations.
The Chainbridge Hotel and Wild Pheasant Hotel just outside the town are more up-market.
Carry on along the A539 - you'll end up going through the scenic horse-shoe pass, though avoid this if you don't like heights!