A cruise on the river Ganga from Kolkata to Varanasi will be launched tomorrow by the West Bengal Tourism DevelopmentCorporation Limited.This will enable the tourists, both from homeand abroad, to revisit the country's colonial past. A specially designed vessel, RV Bengal Pandaw, designed on the lines of a colonial steamer, will take 15 days to sail from Kolkata to Varanasi. According to official sources, this is the first cruise on the Ganges after almost 200 years.