Legoland can be a fun day trip for adults even if you have no kids to accompany you :). If you have grown up playing with Lego blocks or are simply an adult who appreciates how learning can be fun, Legoland will not fail to impress you. I went there with two friends. We went in wondering if the trip would be a waste of our time and came out with a feeling that it was worth the experience.
There is an area called MINILAND within the park where one can see Lego brick models of Danish attractions (Amalienborg palace, Nyhavn, Fredensborg castle, Billund airport) , scenes from movies ( Star Wars, Transformers etc ), Kennedy Space centre, Beverly hills, castle in Scotland. It was impressive to see brick models consisting sometimes of more than 2.1 million lego blocks built over 700-800 hours! There are a number of working models of trains, trucks, traffic, oil production sites etc.
Apart from Miniland, there are also a few rides which are equally fun for adults as well as children. The Polar Express is one such ride.
When you are at Legoland you would want to relax, take it easy and bring out the child in you. Its not a trip worth more than a day ( 4-5 hours ) unless you have kids.