The most popular kind of activities in Delhi are ones relating to relaxation and spirituality. There are dozens of places you can go to for your mind-and-body-cleansing fix of yoga, meditation and massage treatments. Sporting activities are thin on the ground, thanks largely to the heat and pollution, though there are some excellent tours to help get you out and about.
Making a welcome break from the noise and the traffic, Delhi's pockets of green provide an opportunity to wind down, take a stroll or even enjoy a picnic. As well as the public parks, some of the archaeological sites have landscaped grounds that are pretty and peaceful.
Like all of India, Delhi has its fair share of centres for yoga, meditation and massage. Some of the spas are super luxurious, but meditation classes are often free to join, and yoga centres sometimes have free trial classes. Most top-end hotels have their own spas which are also open to nonguests.
There are numerous excellent tours of the city, many of which are guided walking tours around otherwise impenetrable parts of Old Delhi. Some tours are connected to local charities in deprived parts of the city; an excellent way to gain more of an understanding of these organisations if you don't have time to volunteer with them yourself. Cycle tours and motorbike tours are also available.