Nanoscale thermal properties are becoming of extreme importance for modern electronic circuits that dissipate increasing power on the length scale of few tens of nanometers, and for chemical and physical properties sensors and biosensors using nanoscale sized features. While Scanning Thermal Microscopy (SThM) is known for its ability to probe thermal properties and heat generation with nanoscale resolution, until today it was perceived impossible to use it in the liquid environment due to dominating direct heat exchange between microfabricated thermal probe and surrounding liquid that would deteriorate spatial resolution. Nonetheless, our theoretical analysis of SThM in liquids showed that for certain design of SThM probe with resistive heater located near the probe tip, their thermal signal is only moderately affected, by less than half on immersion in a dodecane environment. More significantly, its spatial resolution, surprisingly, would remain practically unaffected, and the thermal contact between the tip apex and the studied sample would be beneficially improved. Our experimental trials of such immersion SThM, or iSThM, were fully successful and here we report for the first time nanoscale SThM measurements of thermal conductivity of Ultra Large Scale Integration polymerceramic metal interconnects with the spatial thermal resolution down to 50 nm. Further studies of heat transport in nanoscale graphite flakes in iSThM suggested, in particular, that highly anisotropic thermal conductivity in graphene layers may play significant role in the nanoscale thermal transport in liquid environment. New iSThM opens a wide range of applications from noncontact measurements of thermal transport in semiconductor devices to exploring graphene energy storage, catalytic reactions and heat generation in biological systems.