This must be one of the tiniest WH sites in the world - it basically consists of just one rather small building in the centre of the pretty town of Lorsch, near Darmstadt. The building, known as the Torhalle or Königshalle - the exact purpose is still a bit of a mystery - is well preserved, considering its age, and it is one of the very few vestiges from the Carolingian era, which was so important for European history. You can go inside and see the upper floor only with a guided tour arranged by the tourist office next to the building - it certainly provided many insights you wouldn't have got from just looking at it from the outside. Most of the frescoes inside are from a later period, but some are from around the time of its construction - a true window into a very distant past. The Altenmünster, featured rather prominently in the name, is really just a foundation wall and nothing more, and about a 15- or 20-minute walk away from the main building (although it is very pleasant walk through fields). This is a very easy site to tick off for collectors, but I would only advise you to visit it in combination with a guided tour - otherwise you will miss a lot. I visited Lorsch on a full day trip from Frankfurt, together with the Messel Pit - easily doable by public transport.