Fitness cramming - which extra activity?

I am the god of hell fire

Hi

Im in need of a leg up the fitness ladder over the next 8 weeks or so in preparation for a big endurance ride

My rising opportunities are OK in that I have 2 opportunities per week for a decent lengthy spin however Im looking to supplement this by doing a couple of other aerobic sessions on an ad hoc basis for an hour or so each
Due to these having to be late at night I would rather not do it outside on the bike, I dont mind night riding but the faff of prep and then locking up makes it a lot less attractive at midnight

Firstly I do not own a turbo and have no (immediate at least) plans to get one

My options must be cost neutral and I have access to the following:

1) Running
2) Rowing machine
3) Exercise bike - decent s/h gym spec offered by mate

Would any of these be of use and if so how best would you exploit them?

Thanks

imposter2.0

how long is the endurance ride ?

Herbsman

use the bike

I am the god of hell fire

Thanks

ride is the Etape - so 140km

I can get 5h on Saturdays and 2h or so one evening midweek

My fitness is "OK" but Id just like to find a bit extra

Riding outside isnt a viable option due to the time slots available and a turbo wouldnt be practical due to issues with storage and noise (water rower so much quieter)

And hoping noone suggests running as I hate it

imposter2.0

Bahzob put up quite a useful post recently about etape training, a lot of which was very sensible (if you can ignore the diversionary pedal technique stuff). Worth doing a search for it..

Zoomer37

Why not get some rollers? Lot less noise + extra hardcore roadie points.

Or if you are looking for an extra activity, get yourself a skipping rope and use that for 20 mins a day. That should increase your genral fitness and will definately help with dropping weight and getting rid of any wobbly bits which in turn will help going up hill in your event. You can take yourself to some right special places if you jump rope correctly and its not going to fatigue your leg muscles as much as say running will so it won't effect your time on the bike.