Puerta del Sol is where this case begins, in the middle of Madrid, with the first clue waiting on the square itself. From there the route works west past Plaza Mayor towards the Royal Palace of Madrid and the Almudena Cathedral beside it. The walk is a detective game rather than a tour: you follow the evidence, and the streets happen to be the setting.

The centre of Madrid is flat, and the stretch between Sol and the palace is one of the busiest parts of the city, which suits groups that do not mind noise around them. It is written for families with children, friends, couples and colleagues, with a team being up to four people sharing a single phone. Larger parties take more tickets and play as separate teams, and there is nothing stopping you from working the case alone. There is no guide and no fixed start time.

How to play

Four steps stand between you and the first clue.

1. Book the City Game
2. Check the instructions email
3. Download the Loquiz app
4. Start playing whenever you like

The case is the murder of Balthasar. Codes have to be broken, photographs taken in the right spot, and the accounts of digital characters weighed against each other. Around the Museo Nacional del Prado and the Thyssen-Bornemisza, where the crowds thin out a little, the alibis begin to conflict and the field of suspects narrows.

Two or more teams turn the whole thing into a race for points, which is why it also works as a teambuilding exercise. Break for lunch, come back to the trail afterwards, and close the case wherever in Madrid you happen to be standing.