Wi-Fi hotspots are a valuable resource for people on the go, especially tourists, as they provide a means to connect personal devices to the Internet. This extra connectivity can be helpful in many situations, e.g., to enable map and chat applications to operate outdoors when cellular connectivity is unavailable or is expensive. Retail stores and many public services have recognized that hotspots have potential to attract and retain customers, so many of them offer free and open Wi-Fi. In busy cities, with many locals and visitors, the number of hotspots is very significant. Some of these hotspots are available for long periods of time, while others are short-lived. When we have many users with devices collecting hotspot observations, they can be used to detect the location -- using the long-lived hotspots -- and to prove the time when the location was visited -- using the short-lived hotspots observed by others users at the location. In this article, we present a dataset of collected Wi-Fi data from the most important tourist locations in the city of Lisbon, Portugal, over a period of months, that was used to show the feasibility of using hotspot data for location detection and proof. The obtained data and algorithms were assessed for a specific use case: smart tourism. We also present the data model used to store the observations and the algorithms developed to detect and prove location of a user device at a specific time. The Lisbon Hotspots dataset, LXspots, is made publicly available to the scientific community so that other researchers can also make use of it to develop new and innovative mobile and Internet of Things applications.