FRA, DUS and now CGN are served by ICE stations, whereas STR, MUC, HAJ, HAM, THF and SXF have direct local or urban rail / metro links.
HAM hasn't (it's being built though), but
- BRE (light rail/streetcar/tramway)
- NUE (underground)
- FDH (!) (local rail) and
- LEJ (intercity rail)
all have. And it's equally true that where there is no rail link, airports tend to have adequate bus connections to/from the area they serve - even if we're talking small and/or low cost outfits such as HHN, LBC, SCN, DTM, FMO, FKB...
In all fairness, however, where public transport to/from the airport is insufficient, it's up to the airline(s) that choose to operate to such airport to set up transport links, or to live with their SLF's ire. Even Luxair had their dedicated bus link to LUX, back when the City Bus didn't serve the airport as frequently as it does now (i.e. until last year).
Ryanair, who know their business, will always set up a bus link to/from whatever remote ex-airbase they
actually fly to, to connect with the place they
allegedly fly to. Some of these are doing a brisk business (HHN/GRE). HLX will simply have to get their act toegther at CVT. Welcome to the real world.
