Or not necessarily on leave, but in some capacity where they were present in numbers but not allowed to fight?
Germans and British combatants frequently visited Ireland which was neutral in WWII. German submarine crews would frequent pubs in Dublin as did RAF pilots and crews of British Navy vessels. Sometimes there would be knowing encounters of Germans and British; sometimes unknowing encounters; sometimes just vague suspicions that the bunch of square-heads sitting at the bar were German submariners. This wasn't the proper venue for violence so visiting belligerents either avoided each other or talked shop with each other. Under Article 17 of the Hague Convention belligerent vessels or aircraft requiring repairs or with sick, wounded or dead crewmen on board could stay in neutral ports for a period of 72 hours. After that time internment of ship and crew would occur. To avoid internment, belligerent ships and aircraft had to leave the neutral country after the prescribed time had elapsed. Ireland has a long history of allowing aircraft of belligerent nations to overfly Irish territory or to refuel at Shannon. The prerequisites were: no weapons, no armaments on board, no explosives. Allied pilots frequently landed in Ireland or crash-landed, refueled or hospitalized and were then escorted to the border with Northern Ireland. Crews of German aircraft had to prove they were not on a 'combative mission' which was a hard test for them, but not impossible. I should note here that ROI neutrality was never a statutory matter of law. It was a policy of the government then in power. So internment or no internment was decided on an ad hoc basis.