Ukraine has lifted travel restrictions and many nationalities no longer require visas. EU citizens and British citizens do not require a visa but are subject to the 90 day out of 180 days rule. Citizens of the EU can enter Ukraine as many times as you want providing your stay is no more than 90 days in any 180 day period. So this means you can stay in Ukraine for 3 months but you will have to wait another 3 months before your return. Citizens of Switzerland, United States, Japan, Norway, Iceland and many other countries share the same entry requirements as EU citizens. Please check all visa requirements on the Ministry of Foreign Affairs of Ukraine.