If you are looking for a monument tour in delhi which stands still throughout the heat, rain, and storm and gives you gimps of Mughal era, look no further than Human's tomb. this tomb (maqbara) is surrounded by a lush green vegetation and trees. This is one of the properly maintained monuments in Delhi I think.
Entry is open from : 6:00 am to 6:00 pm, all days of the week (do check before going as timing may be changed now). If you ask about my personal experience, then I will suggest that go either in the morning to watch the sunrise or in the evening and watch the sunset by river Yamuna in best choice.