Lothal -- literally "mound of the dead" -- is one of the most important sites of the Indus Valley Civilisation, dating back about 4,500 years. Located about 80 km from Ahmedabad, it features the remains of what may be the world's oldest known dock, along with streets, houses, and a drainage system that speaks to remarkably advanced urban planning.
The small on-site museum has artefacts from the excavations, including seals, beads, and pottery. The site itself can be covered on foot in an hour or two. Bring your own food and water -- there are no facilities.
Getting there is part of the adventure. The best option is your own vehicle. You can also take the morning train from Ahmedabad towards Bhavnagar, get off at Lothal-Bhurkhi station, and take an auto-rickshaw. The return is trickier -- plan ahead, as public transport is very limited. Despite the logistical challenges, Lothal is a fascinating and worthwhile visit for anyone interested in ancient history.