The Village of Hommalet
The owner of the local inn had asked you to deal with the rats in the basement. The old floor broke as you stepped on it, dropping you into a small cave system. It turned out to be where, centuries in the past, a wizard had used it as a research lab. There you had fought some skeletons, found a magic sword with "In case of emergency" written on it and a weird spider in a magic circle. It had tried to get you to break it, but well, you weren't going to trust a random talking spider. It was an imp that you dealt with. Then you managed to get out and the innkeeper paid you more for the trouble and free ale.