Throughout 11 television shows and 13 movies, the characters of the Star Trek franchise have visited a number of amazing planets, but some of them have been quite dangerous. Many of those visits resulted in friendly encounters with locals or new Federation allies, but the outcome isn't always certain. When approaching an undiscovered planet, Starfleet officers often have no idea what sort of situation they may be walking into. Scans and video footage can only depict so much. To really explore a planet, an away team has to beam down and get their boots dirty, which, of course, comes with no small amount of risk.
It's true that many of the strange new worlds visited across the Star Trek franchise would make wonderful vacation destinations, but others are far less welcoming. These perilous planets cost many people their lives, sometimes including highly trained Starfleet officers and decorated captains. Whether they have inhospitable weather conditions or hostile inhabitants, some planets should simply be avoided at all costs.
10 Romulus 
Even before its destruction, Romulus would have been a dangerous planet to visit. While there was nothing remarkably dangerous about the climate of Romulus, the fact that it was the homeworld of the Romulans made it a hazardous destination. An offshoot of the Vulcans, the Romulans have been enemies of the Federation since their first appearance in Star Trek: The Original Series episode "Balance of Terror." Notoriously secretive and duplicitous, the Romulans even managed to keep their appearance a mystery until they revealed themselves to Captain Kirk and the crew of the Enterprise. Being on the Romulans' home planet would mean being surrounded by enemies with no idea who to trust. Though the Federation did initially try to help evacuate Romulus before their star went supernova, many in the Federation still find it difficult to trust the remaining Romulans.
