The hippie trail (also the overland) was an overland journey taken by members of the hippie subculture and others from the mid-1950s to the late 1970s travelling from Europe and West Asia through South Asia via countries such as Afghanistan, Pakistan, India, Nepal, Sri Lanka, Bangladesh to Thailand.
A Singaporean passport is the strongest in the world. It gets you access to 193 countries, so everywhere but NorK or Somalia. Japan, South Korea, and most of the EU are close follow ups, although I don’t know how well Schengen passports would do in either Iran or Afghanistan right now. Probably best not to navigate through Kashmir right now either regardless of where your passport is from.