The nearest airport is Erfurt-Weimar Airport, which is located in the state capital Erfurt. Please check if this airport can be used for your travel planning. We can recommend you to travel via the airports in Frankfurt/Main (FRA), Leipzig/Halle (LEJ) or Berlin (BER); from there are convenient train connections (ICE) via Erfurt to Ilmenau. From Leipzig/Halle to Erfurt you need about 1.5 hours by train, from Berlin about 2.5 hours and from Frankfurt about 3 hours.
From Erfurt you can use connecting trains to Ilmenau. The travel time for this is about 1 hour. Of course, you can also cover the remaining approx. 45 km by car or cab. In this case, we recommend that you use the A71 federal highway and exit 15 "Ilmenau-Ost".